Directory UMM :Data Elmu:jurnal:J-a:Journal of Economic Psychology:Vol21.Issue5.2000:
Journal of Economic Psychology 21 (2000) 465±479
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A psychological approach to individual dierences in
intertemporal consumption patterns q
Hermann Brandst
atter
a
a,*
, Werner G
uth
b
Johannes-Kepler-University, Linz, Austria
Humboldt-University, Berlin, Germany
b
Received 13 May 1997; received in revised form 1 August 2000; accepted 13 August 2000
Abstract
When people decide about saving and consumption across the various periods of their
lifetimes, they take into account their life expectancies when comparing present future needs
and resources for satisfying them. The experimental design, applied to two sites (HumboldtUniversity, Berlin and Johannes-Kepler-University, Linz), aims at simulating a sequence of
atleast three, at most six saving vs consumption decisions, depending on a stochastic manipualtion of changes in life expectancy. In this report, we focus on how personality characteristics in¯uence the amount of consumption in single periods of life depending on life
expectancy changes which may render previous consumption rates too low or too high. According to J.A. Gray (The Psychology of Fear and Stress, second ed., Cambridge University
Press, Cambridge, 1987), it was predicted and found that unstable introverts respond most,
and stable extroverts least, to this kind of `punishment'. In addition, some exploratory ®ndings
involving the personality dimensions of self-control and tough-mindedness are reported. Ó 2000 Elsevier Science B.V. All rights reserved.
PsycINFO classi®cation: 3120; 2223; 3920
q
A preliminary version of the paper was presented at the IAREP workshop on Individual Dierences in
Economic Behaviour and Games. International Center for Economic Research (ICER), Torino, 13±14
March 1998.
*
Corresponding author. Tel.: +43-732-2468-225; fax: +43-732-2468-9315.
E-mail address: h.brandstaetter@jk.uni-linz.ac.at (H. BrandstaÈtter).
0167-4870/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 4 8 7 0 ( 0 0 ) 0 0 0 1 4 - 3
466
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
JEL classi®cation: H3
Keywords: Experimental economics; Personality; Intertemporal consumption and saving;
Individual dierences
1. Introduction
Saving behavior is crucial for economic development and, therefore, an
obvious topic for experimental studies (see, for a survey, Anderhub & G
uth,
1999). Macroeconomically, saving reduces consumption and thereby employment, but it may also inspire investment demand via an increased capital
supply which, in the short and long run, osets its direct detrimental eect on
present employment. In microeconomics, deterministic and stochastic life
cycle models (see Hall, 1978, for a survey) have been constructed which assume that people rely on intertemporal utility functions in choosing their
consumption patterns over lifetime. Psychologically, saving, or, more generally, intertemporal decision tasks, can be viewed as intrapersonal decision
con¯icts (see, for instance, Frank, 1996). A saving pattern is an attempt to
balance present and future needs, i.e., a way to resolve the con¯ict between
one's present and future ego.
As it is often dicult, if not impossible, to test such models by ®eld data,
what seems to be possible at most is to validate or reject certain requirements
for intertemporal utilities, like their consistency over time. This quite naturally leads to attempts to analyze saving behavior experimentally. Here we do
not want to look at all the evidence, but focus on a particular study which
also asked the participants to answer the 16PA personality questionnaire
(Brandst
atter, 1988) allowing us to test some hypotheses about saving behavior derived from personality theory.
2. Method
2.1. The saving game
In this computerized experiment, participants (students) had to play 12
rounds of a `saving game' (Anderhub, G
uth, M
uller & Strobel, in press). In
each game, one is given an initial endowment of 11.92 experimental currency
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
467
units (`ECU'), which one can spend in the course of the saving game. Participants know that a `life' lasts for at least three and for at most six periods.
How long it actually lasts depends on chance moves. Before the game starts,
the participants are informed that the probability of reaching the periods 4, 5,
and 6 depended on chance in the following way: there are three dice, a red, a
yellow, and a green one. The meaning of the colors will be explained later.
After having decided about the amount C1 of money to be spent in the ®rst
period, one of the three dice is eliminated, with a probability of 1/3. After the
second move (deciding about consumption C2 in period 2), one of the remaining two dice is eliminated with a probability of 1/2. Therefore, a red, a
yellow, or a green die is left for determining survival beyond periods 3, 4 and 5.
If the green die is left, the good one, life ends after period 3 only when the
number 1 (out of 6) comes up (survival probability of 5/6). The yellow die
ends life with the numbers 1 or 2 (survival probability of 4/6). The ugly red
die brings life to an end with the numbers 1, 2 or 3 (survival probability of 3/
6). The remaining die is applied for moving (or not moving) from period 3 to
period 4, from period 4 to period 5, and from period 5 to period 6.
Assuming that the participants understand the instructions, they know
right from the beginning that the probabilities of survival after period 3
change from an initial probability of 2/3 5=6 4=6 3=6=3 8=12, depending on a random selection of die. If the green die is eliminated ®rst, the
survival probability decreases to 7/12 4=6 3=6=2. If the red die is eliminated ®rst, the survival probability increases to 9/12 5=6 4=6=2. The
initial elimination of the yellow die does not change the survival probability
5=6 3=6=2 8=12. The survival probabilities change again when one of
the remaining two dice is eliminated. Depending on the die ®nally left, the
survival probabilities are 6/12 (red), 8/12 (yellow), and 10/12 (green).
Although the (updated) termination probabilities (the instruction did not
speak of probabilities, but only of termination numbers of the dice) are easily
derived, it is practically impossible to compute the saving pattern maximizing
the intertemporal utility function.
2.2. Permutations of the elimination sequence (green±yellow±red)
There are six permutations of the green±yellow±red sequence of dice
elimination. The order of permutations is randomly varied for each participant, and each participant plays the six permutations twice (two cycles of
games, each cycle in a dierent random order of permutations), altogether 12
rounds.
468
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
2.3. Intertemporal utility function
The participant `earns' ECU-units equivalent to the product of the periodic
consumption levels Ct in the experienced periods t (up to six periods).
UP C1 C2 CT :
Here, T is the stochastically determined length of life with T 3, 4, 5, or 6. In
case of T < 6, all the money kept for the time after period T is lost. On the
other hand, leaving too little or even nothing for the last period T results in a
low payoff UP , or even UP 0.
The intertemporal utility function is psychologically meaningful insofar as
it prompts the players to ®nd a good compromise between equality of consumption across all six periods (which would maximize utility and, of course,
avoid `dying from starvation', if `life' actually lasted six periods) and
spending all the money over the lifetime.
Since a participant experiences 12 successive `lives', one has to specify how
the 12 payos UP in runs 1±12 of the saving game determine his/her monetary
win. Instead of imposing a monetary win (either the average of 12 payos UP
or a randomly selected value UP ), participants were asked to choose for
themselves which payment they preferred.
2.4. Participants
The experiments were run (mostly with students of economics or business
administration) at two sites, at the Humboldt University (Berlin) with 50
participants, and at the Johannes-Kepler-University (Linz), with 117 subjects. There were minor dierences between the Berlin and Linz procedures
which can be neglected in the present context.
2.5. Personality scales
Before playing the 12 rounds of the saving game, the participants are asked
to ®ll out the 16PA-personality adjective scale designed by Brandstatter
(1988) as a short measure of Cattell's ®ve global personality dimensions, viz.,
self-control, emotional stability (the opposite of neuroticism), independence,
tough-mindedness, and extroversion (cf. Schneewind, Schr
oder & Cattell,
1983; Russell & Karol, 1994). When answering this personality questionnaire, participants must locate themselves on 16 dimensions, each represented
by two bipolar scales to achieve a higher reliability of the measures and to
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
469
allow internal consistency checks. We propagate its general use since it
provides some control of what kind of people participate in the study and
since it allows, as demonstrated here, to account in a systematic way for
individual dierences in behavior. Four of the ®ve global dimensions are used
in the present experiment: self-control, emotional stability, extroversion, and
tough-mindedness. For each global dimension, two examples of adjectives
are given:
Self-control
Careless
Uncontrolled
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Conscientious
Self-disciplined
Emotional stability
Easily upset
1 2
3
4
5
6
7
8
9
Self-doubting
1
2
3
4
5
6
7
8
9
Emotionally
stable
Self-assured
Extroversion
Impersonal
Restrained
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Outgoing
Lively
Tough-mindedness
Sensitive
1
Imaginative
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Thick-skinned
Down-to-earth
2.6. Participants' perceptions of the experimental situation
The eects of personality characteristics on game behavior are supposed to
be mediated by the way people perceive the experimental situation. Therefore, after ®nishing the game, the participants were asked to indicate on
adjective rating scales (Brandst
atter, 1990) how they had experienced the
game situation. The 28 bipolar adjectives represent two global dimensions of
situation perception.
Pleasant activation
Boring
1
Unpleasant
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Interesting
Pleasant
Mastery
Dicult
Confused
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Easy
Clear
1
1
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H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
The reliabilities (Cronbach alpha) of the global personality and situation
perception scales are around 0.80. 1
3. Hypotheses
How can we explain the widely varying intertemporal consumption patterns by taking into account the interplay between the structure of the situation as given by the experimental design and the structure of the personality
assessed by the 16PA?
If someone has spent much in the ®rst and second period and realizes
that ®nally the green die will be applied for determining survival beyond
period 3, s/he is supposed to feel punished by his/her fate, just like someone
who has spent little in the early periods and realizes later that the red die
will determine his/her survival. The reaction towards this kind of `punishment' should be a change in spending (spending more or spending less) in
period 3.
Now, we have to ask whether personality theory suggests dierential
reactions to such punishment. Gray (1987) postulates, referring to research
on neuro-physiological processes involved in responses to reward and
punishment, that introverts will be more responsive to punishment than
extroverts, more so when emotional stability is low. According to Gray
(1987, p. 350 f.), no dierence is expected between stable introverts and
unstable extroverts in sensitivity to punishment. In our context, being more
responsive to punishment means showing more pronounced changes in
behavior, i.e., in spending more in period 3 if the red die is applicable, and
spending less, if the green die determines the life expectancy. Gray's model
implies a kind of interaction between emotional stability (the opposite of
neuroticism) and extroversion which leaves the order of the eects, but not
their magnitudes, unchanged. Fig. 1 has been inspired by Fig. 14.6 in Gray
(1987, p. 351). It shows that emotionally unstable introverts are most, and
emotionally stable extroverts least responsive to punishment, and that the
dierence within the two groups of introverts is larger than that between
the two groups of extroverts.
1
English translations of the complete personality adjective list (16PA) and of the situation adjective list
(SITAD) can be requested from the ®rst author.
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
471
Fig. 1. Theoretical prediction of participants' reaction to `punishment' as a function of personality
structure.
The two basic dimensions ± emotional stability and extroversion ± can be
derived as global (second-order) factors from Cattell's 16 personality dimensions (according to which the short adjective version 16PA has been
designed by Brandst
atter, 1988).
A second hypothesis refers to the subjects' choice of the modus of payment, the average payo across all 12 rounds or the payo of a single, randomly selected round. It is assumed that people high on the global
personality dimension `self-control' (they describe themselves as conscientious and self-controlled) prefer the average to the random choice of an
outcome as payo, because they shun higher risks. Participants low in selfcontrol are supposed to opt for the random mode of payment because of
their risk-proneness, possibly also because they can attribute an eventual
failure to bad luck, thus relying on an ego-defensive attitude, which appears
to be rather typical for low self-control people.
4. Results of hypotheses testing
There are two sections of results. The ®rst focuses on hypotheses testing;
the second reports some additional results of exploratory analyses.
472
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
4.1. Payo modus
Let us start with the rather simple second hypothesis: people high on selfcontrol prefer the average of all 12 runs, people low in self-control choose the
random selection of one run. This is indeed true. Averaged across the two
experiments (Berlin and Linz), which show the same pattern of results, only
56% of the participants low in self-control (below median) chose the less risky
averaging payoff format, whereas 80% of the people high in self-control
decided for this format (v2 20.07, p 0:000). The effect size (mean difference divided by the within-group standard deviation) is quite substantial
(d 0:53).
4.2. Reaction towards `punishment'
We expected with hypothesis 1 that anxious subjects (emotionally unstable
introverts) are more, and stable extroverts less sensitive to punishment. Denote by Cit the average consumption in period t for permutation i (see
Table 1). The hypothesis claims a contrast, i.e., a difference of differences in
average consumption, namely,
x C51 C52 C61 C62 =4 ÿ C53 C63 =2
ÿ C11 C12 C21 C22 =4 ÿ C13 C23 =2:
x [(average consumption in the ®rst two periods of permutations 5 and 6)
minus (average consumption in the third period of permutations 5 and 6)]
minus [(average consumption in the ®rst two periods of permutations 1 and
2) minus (average consumption in the third period of permutations 1 and 2)].
This dierence of dierences indicates the strength of the participant's
sensitivity to `punishment' as it is realized with the dierent elimination
Table 1
Permutations of the sequence of dice elimination
Permutations
Eliminated after ®rst period
Eliminated after second period
Remaining die
1
2
3
4
5
6
Green
Yellow
Red
Yellow
Green
Red
Green
Red
Yellow
Red
Green
Yellow
Yellow
Red
Green
Red
Yellow
Green
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
473
sequences of the green, yellow or red die. Instead of this kind of dierence
scores, 2 we use dierences of standardized residuals as dependent variables in
testing the eects of personality (emotional stability and extroversion) on
sensitivity to punishment. This implies predicting C53 C63 =2 from
C51 C52 C61 C62 =4, and predicting C13 C23 =2 from C11 C12
C21 C22 =4, computing the standardized residuals (zresid) and calculating
dierence x zresidC13 C23 =2 minus zresid C53 C63 =2. The higher the
difference score, the stronger the effect of punishment. A difference score of zero
comes up if a participant chooses under permutations 1 and 2 (the survival
probability is that of the red die) as well as under permutation 5 and 6 (the
survival probability is that of the green die) just that consumption in period 3
which would be predicted from the consumption rates of the preceding periods
1 and 2. Negative difference scores point to inconsistent reactions: not properly adjusting expenditures to the situation given with the red or green die. 3
It is claimed that x, represented on the vertical axis of Fig. 1, is larger for
introverts than for extroverts, and larger for emotionally unstable than stable
participants. Fig. 2 presents the results, separately for the ®rst and second
cycle, then combined for both cycles of both the Berlin and the Linz studies,
because both studies came up with the same pattern of effects. It shows that
stable extroverts are indeed least sensitive to punishment in both cycles. A 2
(low vs high stability) by 2 (low vs high extroversion) by 2 (®rst vs second
cycle) ANOVA, with cycle as within subject factor, results in a marginally
signi®cant main effect of emotional stability, F 1; 163 2:80; p 0:096;
g2 0:017, and a signi®cant main effect of extroversion, F 1; 163 5:28;
p 0:023; g2 0:031. There is no signi®cant interaction between emotional
stability and extroversion (p > 0:30), although emotional stability makes a
larger difference in extroverts than in introverts. The effects are stronger in
the second cycle than in the ®rst cycle, F 1; 163 9:52; p 0:002. There is
no signi®cant interaction of stability or extroversion with cycle (p > 0:30).
5. Results of exploratory analyses
The results reported in this section do not refer to theoretical predictions
but have been selected out of various exploratory analyses if they met the
2
Contrary to dierences of residuals, simple dierences do not separate `real' dierences from
regression artefacts (cf. Petermann, 1978).
3
We apologize for this complicated description of our approach to a rather complex set of data.
474
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
Fig. 2. Reaction towards `punishment' as a function of personality structure: (A) ®rst cycle; (B) second
cycle; (C) both cycles combined.
following three criteria: (a) they are signi®cant (p < 0:01, however without
alpha-adjustment for post hoc comparisons), (b) they make sense in post hoc
interpretations, and (c) they are consistent across the two studies (Berlin and
Linz) as well as within the studies across the two cycles. We think that they
deserve some attention even if their statistical signi®cance is questionable due
to the post hoc comparison strategy.
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
475
5.1. Tough-mindedness
Exploring additional relationships between personality characteristics and
adjustments to changes in life expectancy (operationalized as sensitivity to
punishment), we found a consistent eect of the dimension tough-mindedness. Remember, tough-minded people (N 88) describe themselves as
tough-minded (Iÿ), realistic and rational (Mÿ). They respond more strongly
to unexpected changes in `survival' probabilities than tender-minded people
N 79 in both cycles (M 0:05 vs M ÿ0.37, SD 1.01 vs SD 1.47 in
the ®rst cycle: M 0:35 vs M ÿ0:08, SD 0.98 vs SD 1.33 in the second
cycle), and the same pattern of results appears in both experiments. Taking
an average across both cycles gives a dierence with F 1; 165 6:99;
p 0:009.
5.2. Dependence of payo on dierence score
Fig. 3 presents payo as a function of the dierence score for both cycles
combined. Collapsing the two cycles is justi®ed by the fact that the shape of
the curve is basically the same in both cycles. Payo is highest around a
dierence score of x 0:8. Of course, not properly adjusting one's consumption to changes in survival probabilities diminishes the payo.
Fig. 3. Payo as function of sensitivity to punishment. Estimated payo 26:39 0:83x ÿ 0:54x2 ;
R2 0:06.
476
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
Table 2
Payo dependent on personality structure and cycle
Stability
Extroversion
Cycle
N
M
SD
Low
Introvert
1
2
1
2
36
36
49
49
26.49
25.03
26.59
25.31
7.47
6.46
8.80
7.36
1
2
1
2
41
41
41
41
26.46
26.82
23.29
26.22
7.78
7.76
6.95
8.34
Extrovert
High
Introvert
Extrovert
Extroverts, in particular stable extroverts, lack this adjustment because ±
this was our theoretical prediction ± they are less responsive to punishment
(Fig. 2). This explains why stable extroverts get a payo about one-third of a
standard deviation less than average in the ®rst cycle (cf. Table 2).
5.3. Learning from the experience of the ®rst cycle
People generally show a stronger response to unexpected changes in survival probabilities in the second cycle than in the ®rst cycle,
F 1; 163 9:52; p 0:002; g2 0:055 4 (Fig. 2). This change is particularly visibe in unstable introverts and stable extroverts, although the higherorder interaction (cycle by emotional stability by extroversion) is not signi®cant (p > 0:10). As a consequence of those adjustments, extroverts, in
particuar stable extroverts, improve their payos from the ®rst to the second
cycle, whereas introverts do not, possibly because they overreact to punishment in the second cycle. The interaction cycle by stability is signi®cant,
F 1; 163 5:85; p 0:017; g2 0:035. The variance attributed to this
interaction derives mainly from the payoff increase of the stable extroverts.
6. Discussion
In both cycles (remember, a cycle is a run of six permutations), emotionally
unstable introverts are most sensitive to punishment, whereas emotionally
stable extroverts are least sensitive (Fig. 2). This is in line with our predictions
4
g2 is reported as a measure of eect size.
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
477
derived from the theory of Gray (1987, p. 350 f.), which also states that there
is no dierence between stable introverts and unstable extroverts in sensitivity
to punishment, and that both groups are between (the most sensitive) unstable introverts and (the least sensitive) stable extroverts. According to
Gray's model, the polarity introversion±extroversion determines whether a
person is more sensitive to punishment or more sensitive to reward, and
neuroticism is conceived as a kind of multiplicative factor augmenting the
sensitivity to punishment or reward, respectively. This implies a kind of interaction between neuroticism and extroversion which should result in larger
dierences of punishment eects between unstable and stable introverts than
between unstable and stable extroverts. In our data, however, emotional
stability increases the dierence in extroverts. Although interaction stability
by extroversion is not signi®cant, this pattern of results is not in line with the
model of Gray.
We may ask why, in the saving game, the dierence in sensitivity to
punishment between unstable and stable introverts is not larger than that
between unstable and stable extroverts. An answer may be found in the
participants' ratings of how they had perceived the experimental situation.
From the 28 adjective rating scales, two dimensions were derived labeled as
pleasant activation (with marker variables interesting, pleasant) and mastery
(easy, clear). Only stable extroverts have high scores on pleasant activation
(the eect size of the contrast between stable extroverts and the other three
groups is d 0:32), 5 and, on average, stable extroverts are also least sensitive to punishment. Perceiving the game as a stimulating and pleasant experience seems to make participants less sensitive to punishment.
Still, we do not know why the unstable introverts experienced the situation
no more negatively than the stable introverts and the unstable extroverts. The
answer could be found in the second dimension which we called `mastery':
introverts, whether unstable or stable, have higher scores on mastery than
extroverts, i.e., they ®nd the game easier and better to comprehend. Here one
may refer to the ®nding that introverts tend to have better school marks and
higher performance scores in cognitive tests (Brandstatter, 1997). If they
indeed have a better understanding of the game and of how more money
can be earned, they will rationally restrain themselves from too strong reactions to `punishment' which would diminish their payo, thus keeping the
5
The dierence in pleasant activation between the other three groups (unstable introverts, stable
introverts, and unstable extroverts) are minimal.
478
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
dierence between unstable and stable introverts in their responses to punishment in the present experiment at a moderate level. Fig. 3 shows that, on
an average across cycles, payos reach their maximum around a dierence
score of 0.80.
Participants react less to changes of life expectancy, i.e., to `punishment' in
the ®rst cycle. Obviously, the participants have learned to respond more
adequately to stochastic changes in life expectancy. We may also assume that
the decisions in the ®rst cycle are somewhat more erratic than those in the
second cycle. If so, the data of the second cycle are better suited to test Gray's
model, and the results of the second cycle are also in better agreement with
the theoretical model.
Sensitivity to reward, in Gray's model lowest in stable introverts and
highest in unstable extroverts, is not an issue in our experiment, because
reward, i.e., starting with high consumption and ®nding out that the red die
will ®nally be applied (permutations 1 and 2), or starting with low consumption and ®nding out that the green die will determine the life expectancy
(permutations 5 and 6), does not imply any impetus for change. Without a
pressure for change, however, we cannot expect any dierential eects of
personality structure.
That tough-minded (realistic and rational) people adjust their decisions
more clearly to changes in survival probabilities makes sense. Their behavior
comes close to what economic rationality would prescribe.
7. Conclusion
Four of the ®ve global personality dimensions (second-order factors of
Cattell's system of personality measures), i.e., self-control, emotional stability, tough-mindedness, and extroversion, proved useful in explaining intertemporal saving and consumption decisions. Although eect sizes as
indicated by the percentages of variance explained by the independent variables (g2 ) are modest, the consistency of the results across replications (Berlin
and Linz) and across cycles within the replications gives them some importance in testing and further developing theoretical ideas in an attempt to
explain intertemporal consumption decisions. It seems worthwhile to include
short, but nevertheless comprehensive and basic, measures of personality as
well as measures of situation perception in future experiments on economic
behavior.
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
479
Acknowledgements
The authors thank Vital Anderhub, Wieland M
uller, and Martin Strobel
(Humboldt University) and Willy Kriz (Johannes-Kepler-University) for
their contributions in planning, running and analyzing the experiment. See
Anderhub et al. (in press) for a detailed report on the experiment which did
not refer to the individual dierences.
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Russell, M. T., & Karol, D. L. (1994). The 16PF ®fth edition administrator's manual (2nd ed.). Champaign,
IL: Institute for Personality and Ability Testing.
Schneewind, K. A., Schr
oder, G., & Cattell, R. B. (1983). Der 16-Pers
onlichkeits-Faktoren-Test 16PF [The
16-Personality-Factor-Test. 16PF]. Bern: Huber.
www.elsevier.com/locate/joep
A psychological approach to individual dierences in
intertemporal consumption patterns q
Hermann Brandst
atter
a
a,*
, Werner G
uth
b
Johannes-Kepler-University, Linz, Austria
Humboldt-University, Berlin, Germany
b
Received 13 May 1997; received in revised form 1 August 2000; accepted 13 August 2000
Abstract
When people decide about saving and consumption across the various periods of their
lifetimes, they take into account their life expectancies when comparing present future needs
and resources for satisfying them. The experimental design, applied to two sites (HumboldtUniversity, Berlin and Johannes-Kepler-University, Linz), aims at simulating a sequence of
atleast three, at most six saving vs consumption decisions, depending on a stochastic manipualtion of changes in life expectancy. In this report, we focus on how personality characteristics in¯uence the amount of consumption in single periods of life depending on life
expectancy changes which may render previous consumption rates too low or too high. According to J.A. Gray (The Psychology of Fear and Stress, second ed., Cambridge University
Press, Cambridge, 1987), it was predicted and found that unstable introverts respond most,
and stable extroverts least, to this kind of `punishment'. In addition, some exploratory ®ndings
involving the personality dimensions of self-control and tough-mindedness are reported. Ó 2000 Elsevier Science B.V. All rights reserved.
PsycINFO classi®cation: 3120; 2223; 3920
q
A preliminary version of the paper was presented at the IAREP workshop on Individual Dierences in
Economic Behaviour and Games. International Center for Economic Research (ICER), Torino, 13±14
March 1998.
*
Corresponding author. Tel.: +43-732-2468-225; fax: +43-732-2468-9315.
E-mail address: h.brandstaetter@jk.uni-linz.ac.at (H. BrandstaÈtter).
0167-4870/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 4 8 7 0 ( 0 0 ) 0 0 0 1 4 - 3
466
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
JEL classi®cation: H3
Keywords: Experimental economics; Personality; Intertemporal consumption and saving;
Individual dierences
1. Introduction
Saving behavior is crucial for economic development and, therefore, an
obvious topic for experimental studies (see, for a survey, Anderhub & G
uth,
1999). Macroeconomically, saving reduces consumption and thereby employment, but it may also inspire investment demand via an increased capital
supply which, in the short and long run, osets its direct detrimental eect on
present employment. In microeconomics, deterministic and stochastic life
cycle models (see Hall, 1978, for a survey) have been constructed which assume that people rely on intertemporal utility functions in choosing their
consumption patterns over lifetime. Psychologically, saving, or, more generally, intertemporal decision tasks, can be viewed as intrapersonal decision
con¯icts (see, for instance, Frank, 1996). A saving pattern is an attempt to
balance present and future needs, i.e., a way to resolve the con¯ict between
one's present and future ego.
As it is often dicult, if not impossible, to test such models by ®eld data,
what seems to be possible at most is to validate or reject certain requirements
for intertemporal utilities, like their consistency over time. This quite naturally leads to attempts to analyze saving behavior experimentally. Here we do
not want to look at all the evidence, but focus on a particular study which
also asked the participants to answer the 16PA personality questionnaire
(Brandst
atter, 1988) allowing us to test some hypotheses about saving behavior derived from personality theory.
2. Method
2.1. The saving game
In this computerized experiment, participants (students) had to play 12
rounds of a `saving game' (Anderhub, G
uth, M
uller & Strobel, in press). In
each game, one is given an initial endowment of 11.92 experimental currency
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
467
units (`ECU'), which one can spend in the course of the saving game. Participants know that a `life' lasts for at least three and for at most six periods.
How long it actually lasts depends on chance moves. Before the game starts,
the participants are informed that the probability of reaching the periods 4, 5,
and 6 depended on chance in the following way: there are three dice, a red, a
yellow, and a green one. The meaning of the colors will be explained later.
After having decided about the amount C1 of money to be spent in the ®rst
period, one of the three dice is eliminated, with a probability of 1/3. After the
second move (deciding about consumption C2 in period 2), one of the remaining two dice is eliminated with a probability of 1/2. Therefore, a red, a
yellow, or a green die is left for determining survival beyond periods 3, 4 and 5.
If the green die is left, the good one, life ends after period 3 only when the
number 1 (out of 6) comes up (survival probability of 5/6). The yellow die
ends life with the numbers 1 or 2 (survival probability of 4/6). The ugly red
die brings life to an end with the numbers 1, 2 or 3 (survival probability of 3/
6). The remaining die is applied for moving (or not moving) from period 3 to
period 4, from period 4 to period 5, and from period 5 to period 6.
Assuming that the participants understand the instructions, they know
right from the beginning that the probabilities of survival after period 3
change from an initial probability of 2/3 5=6 4=6 3=6=3 8=12, depending on a random selection of die. If the green die is eliminated ®rst, the
survival probability decreases to 7/12 4=6 3=6=2. If the red die is eliminated ®rst, the survival probability increases to 9/12 5=6 4=6=2. The
initial elimination of the yellow die does not change the survival probability
5=6 3=6=2 8=12. The survival probabilities change again when one of
the remaining two dice is eliminated. Depending on the die ®nally left, the
survival probabilities are 6/12 (red), 8/12 (yellow), and 10/12 (green).
Although the (updated) termination probabilities (the instruction did not
speak of probabilities, but only of termination numbers of the dice) are easily
derived, it is practically impossible to compute the saving pattern maximizing
the intertemporal utility function.
2.2. Permutations of the elimination sequence (green±yellow±red)
There are six permutations of the green±yellow±red sequence of dice
elimination. The order of permutations is randomly varied for each participant, and each participant plays the six permutations twice (two cycles of
games, each cycle in a dierent random order of permutations), altogether 12
rounds.
468
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
2.3. Intertemporal utility function
The participant `earns' ECU-units equivalent to the product of the periodic
consumption levels Ct in the experienced periods t (up to six periods).
UP C1 C2 CT :
Here, T is the stochastically determined length of life with T 3, 4, 5, or 6. In
case of T < 6, all the money kept for the time after period T is lost. On the
other hand, leaving too little or even nothing for the last period T results in a
low payoff UP , or even UP 0.
The intertemporal utility function is psychologically meaningful insofar as
it prompts the players to ®nd a good compromise between equality of consumption across all six periods (which would maximize utility and, of course,
avoid `dying from starvation', if `life' actually lasted six periods) and
spending all the money over the lifetime.
Since a participant experiences 12 successive `lives', one has to specify how
the 12 payos UP in runs 1±12 of the saving game determine his/her monetary
win. Instead of imposing a monetary win (either the average of 12 payos UP
or a randomly selected value UP ), participants were asked to choose for
themselves which payment they preferred.
2.4. Participants
The experiments were run (mostly with students of economics or business
administration) at two sites, at the Humboldt University (Berlin) with 50
participants, and at the Johannes-Kepler-University (Linz), with 117 subjects. There were minor dierences between the Berlin and Linz procedures
which can be neglected in the present context.
2.5. Personality scales
Before playing the 12 rounds of the saving game, the participants are asked
to ®ll out the 16PA-personality adjective scale designed by Brandstatter
(1988) as a short measure of Cattell's ®ve global personality dimensions, viz.,
self-control, emotional stability (the opposite of neuroticism), independence,
tough-mindedness, and extroversion (cf. Schneewind, Schr
oder & Cattell,
1983; Russell & Karol, 1994). When answering this personality questionnaire, participants must locate themselves on 16 dimensions, each represented
by two bipolar scales to achieve a higher reliability of the measures and to
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
469
allow internal consistency checks. We propagate its general use since it
provides some control of what kind of people participate in the study and
since it allows, as demonstrated here, to account in a systematic way for
individual dierences in behavior. Four of the ®ve global dimensions are used
in the present experiment: self-control, emotional stability, extroversion, and
tough-mindedness. For each global dimension, two examples of adjectives
are given:
Self-control
Careless
Uncontrolled
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Conscientious
Self-disciplined
Emotional stability
Easily upset
1 2
3
4
5
6
7
8
9
Self-doubting
1
2
3
4
5
6
7
8
9
Emotionally
stable
Self-assured
Extroversion
Impersonal
Restrained
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Outgoing
Lively
Tough-mindedness
Sensitive
1
Imaginative
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Thick-skinned
Down-to-earth
2.6. Participants' perceptions of the experimental situation
The eects of personality characteristics on game behavior are supposed to
be mediated by the way people perceive the experimental situation. Therefore, after ®nishing the game, the participants were asked to indicate on
adjective rating scales (Brandst
atter, 1990) how they had experienced the
game situation. The 28 bipolar adjectives represent two global dimensions of
situation perception.
Pleasant activation
Boring
1
Unpleasant
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Interesting
Pleasant
Mastery
Dicult
Confused
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
Easy
Clear
1
1
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H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
The reliabilities (Cronbach alpha) of the global personality and situation
perception scales are around 0.80. 1
3. Hypotheses
How can we explain the widely varying intertemporal consumption patterns by taking into account the interplay between the structure of the situation as given by the experimental design and the structure of the personality
assessed by the 16PA?
If someone has spent much in the ®rst and second period and realizes
that ®nally the green die will be applied for determining survival beyond
period 3, s/he is supposed to feel punished by his/her fate, just like someone
who has spent little in the early periods and realizes later that the red die
will determine his/her survival. The reaction towards this kind of `punishment' should be a change in spending (spending more or spending less) in
period 3.
Now, we have to ask whether personality theory suggests dierential
reactions to such punishment. Gray (1987) postulates, referring to research
on neuro-physiological processes involved in responses to reward and
punishment, that introverts will be more responsive to punishment than
extroverts, more so when emotional stability is low. According to Gray
(1987, p. 350 f.), no dierence is expected between stable introverts and
unstable extroverts in sensitivity to punishment. In our context, being more
responsive to punishment means showing more pronounced changes in
behavior, i.e., in spending more in period 3 if the red die is applicable, and
spending less, if the green die determines the life expectancy. Gray's model
implies a kind of interaction between emotional stability (the opposite of
neuroticism) and extroversion which leaves the order of the eects, but not
their magnitudes, unchanged. Fig. 1 has been inspired by Fig. 14.6 in Gray
(1987, p. 351). It shows that emotionally unstable introverts are most, and
emotionally stable extroverts least responsive to punishment, and that the
dierence within the two groups of introverts is larger than that between
the two groups of extroverts.
1
English translations of the complete personality adjective list (16PA) and of the situation adjective list
(SITAD) can be requested from the ®rst author.
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
471
Fig. 1. Theoretical prediction of participants' reaction to `punishment' as a function of personality
structure.
The two basic dimensions ± emotional stability and extroversion ± can be
derived as global (second-order) factors from Cattell's 16 personality dimensions (according to which the short adjective version 16PA has been
designed by Brandst
atter, 1988).
A second hypothesis refers to the subjects' choice of the modus of payment, the average payo across all 12 rounds or the payo of a single, randomly selected round. It is assumed that people high on the global
personality dimension `self-control' (they describe themselves as conscientious and self-controlled) prefer the average to the random choice of an
outcome as payo, because they shun higher risks. Participants low in selfcontrol are supposed to opt for the random mode of payment because of
their risk-proneness, possibly also because they can attribute an eventual
failure to bad luck, thus relying on an ego-defensive attitude, which appears
to be rather typical for low self-control people.
4. Results of hypotheses testing
There are two sections of results. The ®rst focuses on hypotheses testing;
the second reports some additional results of exploratory analyses.
472
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
4.1. Payo modus
Let us start with the rather simple second hypothesis: people high on selfcontrol prefer the average of all 12 runs, people low in self-control choose the
random selection of one run. This is indeed true. Averaged across the two
experiments (Berlin and Linz), which show the same pattern of results, only
56% of the participants low in self-control (below median) chose the less risky
averaging payoff format, whereas 80% of the people high in self-control
decided for this format (v2 20.07, p 0:000). The effect size (mean difference divided by the within-group standard deviation) is quite substantial
(d 0:53).
4.2. Reaction towards `punishment'
We expected with hypothesis 1 that anxious subjects (emotionally unstable
introverts) are more, and stable extroverts less sensitive to punishment. Denote by Cit the average consumption in period t for permutation i (see
Table 1). The hypothesis claims a contrast, i.e., a difference of differences in
average consumption, namely,
x C51 C52 C61 C62 =4 ÿ C53 C63 =2
ÿ C11 C12 C21 C22 =4 ÿ C13 C23 =2:
x [(average consumption in the ®rst two periods of permutations 5 and 6)
minus (average consumption in the third period of permutations 5 and 6)]
minus [(average consumption in the ®rst two periods of permutations 1 and
2) minus (average consumption in the third period of permutations 1 and 2)].
This dierence of dierences indicates the strength of the participant's
sensitivity to `punishment' as it is realized with the dierent elimination
Table 1
Permutations of the sequence of dice elimination
Permutations
Eliminated after ®rst period
Eliminated after second period
Remaining die
1
2
3
4
5
6
Green
Yellow
Red
Yellow
Green
Red
Green
Red
Yellow
Red
Green
Yellow
Yellow
Red
Green
Red
Yellow
Green
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
473
sequences of the green, yellow or red die. Instead of this kind of dierence
scores, 2 we use dierences of standardized residuals as dependent variables in
testing the eects of personality (emotional stability and extroversion) on
sensitivity to punishment. This implies predicting C53 C63 =2 from
C51 C52 C61 C62 =4, and predicting C13 C23 =2 from C11 C12
C21 C22 =4, computing the standardized residuals (zresid) and calculating
dierence x zresidC13 C23 =2 minus zresid C53 C63 =2. The higher the
difference score, the stronger the effect of punishment. A difference score of zero
comes up if a participant chooses under permutations 1 and 2 (the survival
probability is that of the red die) as well as under permutation 5 and 6 (the
survival probability is that of the green die) just that consumption in period 3
which would be predicted from the consumption rates of the preceding periods
1 and 2. Negative difference scores point to inconsistent reactions: not properly adjusting expenditures to the situation given with the red or green die. 3
It is claimed that x, represented on the vertical axis of Fig. 1, is larger for
introverts than for extroverts, and larger for emotionally unstable than stable
participants. Fig. 2 presents the results, separately for the ®rst and second
cycle, then combined for both cycles of both the Berlin and the Linz studies,
because both studies came up with the same pattern of effects. It shows that
stable extroverts are indeed least sensitive to punishment in both cycles. A 2
(low vs high stability) by 2 (low vs high extroversion) by 2 (®rst vs second
cycle) ANOVA, with cycle as within subject factor, results in a marginally
signi®cant main effect of emotional stability, F 1; 163 2:80; p 0:096;
g2 0:017, and a signi®cant main effect of extroversion, F 1; 163 5:28;
p 0:023; g2 0:031. There is no signi®cant interaction between emotional
stability and extroversion (p > 0:30), although emotional stability makes a
larger difference in extroverts than in introverts. The effects are stronger in
the second cycle than in the ®rst cycle, F 1; 163 9:52; p 0:002. There is
no signi®cant interaction of stability or extroversion with cycle (p > 0:30).
5. Results of exploratory analyses
The results reported in this section do not refer to theoretical predictions
but have been selected out of various exploratory analyses if they met the
2
Contrary to dierences of residuals, simple dierences do not separate `real' dierences from
regression artefacts (cf. Petermann, 1978).
3
We apologize for this complicated description of our approach to a rather complex set of data.
474
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
Fig. 2. Reaction towards `punishment' as a function of personality structure: (A) ®rst cycle; (B) second
cycle; (C) both cycles combined.
following three criteria: (a) they are signi®cant (p < 0:01, however without
alpha-adjustment for post hoc comparisons), (b) they make sense in post hoc
interpretations, and (c) they are consistent across the two studies (Berlin and
Linz) as well as within the studies across the two cycles. We think that they
deserve some attention even if their statistical signi®cance is questionable due
to the post hoc comparison strategy.
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
475
5.1. Tough-mindedness
Exploring additional relationships between personality characteristics and
adjustments to changes in life expectancy (operationalized as sensitivity to
punishment), we found a consistent eect of the dimension tough-mindedness. Remember, tough-minded people (N 88) describe themselves as
tough-minded (Iÿ), realistic and rational (Mÿ). They respond more strongly
to unexpected changes in `survival' probabilities than tender-minded people
N 79 in both cycles (M 0:05 vs M ÿ0.37, SD 1.01 vs SD 1.47 in
the ®rst cycle: M 0:35 vs M ÿ0:08, SD 0.98 vs SD 1.33 in the second
cycle), and the same pattern of results appears in both experiments. Taking
an average across both cycles gives a dierence with F 1; 165 6:99;
p 0:009.
5.2. Dependence of payo on dierence score
Fig. 3 presents payo as a function of the dierence score for both cycles
combined. Collapsing the two cycles is justi®ed by the fact that the shape of
the curve is basically the same in both cycles. Payo is highest around a
dierence score of x 0:8. Of course, not properly adjusting one's consumption to changes in survival probabilities diminishes the payo.
Fig. 3. Payo as function of sensitivity to punishment. Estimated payo 26:39 0:83x ÿ 0:54x2 ;
R2 0:06.
476
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
Table 2
Payo dependent on personality structure and cycle
Stability
Extroversion
Cycle
N
M
SD
Low
Introvert
1
2
1
2
36
36
49
49
26.49
25.03
26.59
25.31
7.47
6.46
8.80
7.36
1
2
1
2
41
41
41
41
26.46
26.82
23.29
26.22
7.78
7.76
6.95
8.34
Extrovert
High
Introvert
Extrovert
Extroverts, in particular stable extroverts, lack this adjustment because ±
this was our theoretical prediction ± they are less responsive to punishment
(Fig. 2). This explains why stable extroverts get a payo about one-third of a
standard deviation less than average in the ®rst cycle (cf. Table 2).
5.3. Learning from the experience of the ®rst cycle
People generally show a stronger response to unexpected changes in survival probabilities in the second cycle than in the ®rst cycle,
F 1; 163 9:52; p 0:002; g2 0:055 4 (Fig. 2). This change is particularly visibe in unstable introverts and stable extroverts, although the higherorder interaction (cycle by emotional stability by extroversion) is not signi®cant (p > 0:10). As a consequence of those adjustments, extroverts, in
particuar stable extroverts, improve their payos from the ®rst to the second
cycle, whereas introverts do not, possibly because they overreact to punishment in the second cycle. The interaction cycle by stability is signi®cant,
F 1; 163 5:85; p 0:017; g2 0:035. The variance attributed to this
interaction derives mainly from the payoff increase of the stable extroverts.
6. Discussion
In both cycles (remember, a cycle is a run of six permutations), emotionally
unstable introverts are most sensitive to punishment, whereas emotionally
stable extroverts are least sensitive (Fig. 2). This is in line with our predictions
4
g2 is reported as a measure of eect size.
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
477
derived from the theory of Gray (1987, p. 350 f.), which also states that there
is no dierence between stable introverts and unstable extroverts in sensitivity
to punishment, and that both groups are between (the most sensitive) unstable introverts and (the least sensitive) stable extroverts. According to
Gray's model, the polarity introversion±extroversion determines whether a
person is more sensitive to punishment or more sensitive to reward, and
neuroticism is conceived as a kind of multiplicative factor augmenting the
sensitivity to punishment or reward, respectively. This implies a kind of interaction between neuroticism and extroversion which should result in larger
dierences of punishment eects between unstable and stable introverts than
between unstable and stable extroverts. In our data, however, emotional
stability increases the dierence in extroverts. Although interaction stability
by extroversion is not signi®cant, this pattern of results is not in line with the
model of Gray.
We may ask why, in the saving game, the dierence in sensitivity to
punishment between unstable and stable introverts is not larger than that
between unstable and stable extroverts. An answer may be found in the
participants' ratings of how they had perceived the experimental situation.
From the 28 adjective rating scales, two dimensions were derived labeled as
pleasant activation (with marker variables interesting, pleasant) and mastery
(easy, clear). Only stable extroverts have high scores on pleasant activation
(the eect size of the contrast between stable extroverts and the other three
groups is d 0:32), 5 and, on average, stable extroverts are also least sensitive to punishment. Perceiving the game as a stimulating and pleasant experience seems to make participants less sensitive to punishment.
Still, we do not know why the unstable introverts experienced the situation
no more negatively than the stable introverts and the unstable extroverts. The
answer could be found in the second dimension which we called `mastery':
introverts, whether unstable or stable, have higher scores on mastery than
extroverts, i.e., they ®nd the game easier and better to comprehend. Here one
may refer to the ®nding that introverts tend to have better school marks and
higher performance scores in cognitive tests (Brandstatter, 1997). If they
indeed have a better understanding of the game and of how more money
can be earned, they will rationally restrain themselves from too strong reactions to `punishment' which would diminish their payo, thus keeping the
5
The dierence in pleasant activation between the other three groups (unstable introverts, stable
introverts, and unstable extroverts) are minimal.
478
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
dierence between unstable and stable introverts in their responses to punishment in the present experiment at a moderate level. Fig. 3 shows that, on
an average across cycles, payos reach their maximum around a dierence
score of 0.80.
Participants react less to changes of life expectancy, i.e., to `punishment' in
the ®rst cycle. Obviously, the participants have learned to respond more
adequately to stochastic changes in life expectancy. We may also assume that
the decisions in the ®rst cycle are somewhat more erratic than those in the
second cycle. If so, the data of the second cycle are better suited to test Gray's
model, and the results of the second cycle are also in better agreement with
the theoretical model.
Sensitivity to reward, in Gray's model lowest in stable introverts and
highest in unstable extroverts, is not an issue in our experiment, because
reward, i.e., starting with high consumption and ®nding out that the red die
will ®nally be applied (permutations 1 and 2), or starting with low consumption and ®nding out that the green die will determine the life expectancy
(permutations 5 and 6), does not imply any impetus for change. Without a
pressure for change, however, we cannot expect any dierential eects of
personality structure.
That tough-minded (realistic and rational) people adjust their decisions
more clearly to changes in survival probabilities makes sense. Their behavior
comes close to what economic rationality would prescribe.
7. Conclusion
Four of the ®ve global personality dimensions (second-order factors of
Cattell's system of personality measures), i.e., self-control, emotional stability, tough-mindedness, and extroversion, proved useful in explaining intertemporal saving and consumption decisions. Although eect sizes as
indicated by the percentages of variance explained by the independent variables (g2 ) are modest, the consistency of the results across replications (Berlin
and Linz) and across cycles within the replications gives them some importance in testing and further developing theoretical ideas in an attempt to
explain intertemporal consumption decisions. It seems worthwhile to include
short, but nevertheless comprehensive and basic, measures of personality as
well as measures of situation perception in future experiments on economic
behavior.
H. Brandst
atter, W. G
uth / Journal of Economic Psychology 21 (2000) 465±479
479
Acknowledgements
The authors thank Vital Anderhub, Wieland M
uller, and Martin Strobel
(Humboldt University) and Willy Kriz (Johannes-Kepler-University) for
their contributions in planning, running and analyzing the experiment. See
Anderhub et al. (in press) for a detailed report on the experiment which did
not refer to the individual dierences.
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