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3.6 Method of Collecting Data
In doing a research, the researcher should collect data as the object to be organized and analyzed. There are some methods in collecting the data. In this
research, I tried to collect the data by using several methods which were try-out, pre-test, treatments, and post-test.
3.6.1 Try Out
Instrument is the fundamental thing in a research. A good instrument must have validity and reliability. Therefore, I have to try out the instrument before
conducting the test. After I administered the try out, I could analyze the data by finding the validity and reliability. Only valid and reliable instrument could be
used in this research.
3.6.1.1 Validity
Validity is the most complex criterion of an effective test. Grondlund as quoted by Brown 2004: 22 validity is the extent to which inferences made from assessment
results are appropriate, meaningful, and useful in terms of the purpose of the assessment. The formula of the validity is as follow:
Where,
r
xy
= the validity of the item test N
= the number of the students
{ }{
}
2 2
2 2
Y Y
N X
X N
Y X
XY N
r
xy
− −
− =
28
X = the number of students who answer correctly
Y = the students’ score
3.6.1.2 Reliability
Similar to validity, reliability is also the characteristics of a good test. Reliability means the stability of test scores. A reliable test is consistent and dependable. If
the test is given to the same students on two different occasions, the test will show similar results. To determine the reliability of the test, the following formula is
used: −
− −
= kVt
M k
M k
k r
1 1
11
Where, r
11
= reliability of the test k
= the number of the items M
= the means of the scores Vt
= the total of variants
3.6.1.3 Level of Difficulty
Arikunto 1999: 207 states that difficulty level is a number that shows the ease and difficulty of an item. A good test is a test which is not too easy or difficult.
The formula used is as follow Arikunto, 2002:208:
JS B
P =
29
Where, P
= item difficulty B
= the number of students who answered correctly JS
= the total number of the students The criteria of computation are as follow:
Interval Criteria
0.00 P 0.30 Difficult
0.30 P 0.70 Medium
0.70 P 1.00 Easy
3.6.1.4 Discriminating Power
Heaton 1975: 173 argues that the index discrimination tells us those students who perform well on the whole test to do well or badly on each item in the test.
The formula used is as follow Arikunto, 2002:210:
B B
A A
J B
J B
D −
= Where,
D = Discriminating power
B
A
= Number of students in the upper group who answered correctly B
B
= Number of students in the lower group who answered correctly J
A
= Number of all students in the upper group
Table 3.1 Criteria of Level of Difficulty
30
J
B
= Number of all students in the lower group
The criteria of the computation are as follow:
Interval Criteria
D 0.20 Poor
0.20 D 0.40 Satisfactory
0.40 D 0.70 Good
0.70 D 1.00 Excellent
3.6.2 Pre-Test
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