and the children’s scores on developmental assessments. This is done by comparing the full sample with the sample of respondents who have never missed an interview.
Section III examines how attrition affects estimates of the relationship between fam- ily characteristics and the children’s assessment scores. Lastly, Section IV summa-
rizes and discusses the ndings.
II. Attrition Patterns
The analysis of the NLSY79 and NLSY79-C in this study is based on 4,926 women and their 9,460 children whose births are recorded through the
2000 interview.
2
Analysis is done separately for the full sample, that is, all 4926 women and their children, and for the cross-sectional sample which omits the women
in the Black and Hispanic oversamples and their children. The data are unweighted.
3
Table 1 describes the attrition patterns for the women of the NLSY79 by present- ing the rates of attrition and rst-attrition for the full sample and the cross-section.
Attrition has been relatively low among the women of the NLSY79, although it has increased over time. The attrition rates range from 3 percent to 4 percent in the early
years of the survey and from 12 percent to 17 percent in the recent biennial survey- years with the patterns being quite similar for the full-sample of women and the
cross-section. Until the most recent interview, initial attrition was greatest in the second year of the survey when nearly 4 percent of the full-sample and cross-sec-
tional women attrited. In the subsequent years, rst attrition is generally between 1 percent and 2 percent until the 1996 interview. The patterns displayed in this table
show the extent to which attrition has affected the sample of women in the NLSY79, but do not provide information on whether attrition has caused the sample to be
nonrepresentative.
Table 2 compares all person-year observations of the women in the NLSY79 with the annual observations from only those women who have never missed an interview
continuous subsample to assess whether attrition is nonrepresentative along se- lected characteristics that describe the women’s fertility decisions, marital status and
economic status. Fitzgerald, Gottschalk, and Moftt 1998 point out that the appro- priate comparison is between the full sample and the nonattritors, not between the
attritors and nonattritors where attrition may lead to bias in both samples.
Table 2 is organized into two panels. Panel A presents the statistics for the full sample, and Panel B the statistics for the cross-section. In each of the panels, Col-
umns 1-4 present the descriptive statistics for all person-year observations and Col- umns 5-8 for the person-year observations of women in the continuous subsample.
2. Because they have been dropped from the NLSY79, the samples used in this paper exclude women from the armed forces supplement and the supplement of economically disadvantaged whites and their
children. 3. The analysis in this paper on the women in the NLSY79 also was done using the full and cross-sectional
samples weighted by the NLSY79-provided weights and the MaCurdy-Mroz-Gritz cross-sectional weights. The analysis on children’s descriptive statistics Table 4 for the full sample also was conducted using
the NLSY79-C weights. The use of weights does not affect the key ndings so long as the cross-section and the supplemental samples are examined separately, though the levels for some variables family in-
come, AFQT are affected.
Table 1 Attrition Rates for the NLSY79 Women
Attrition First Attrition
Full Cross-
Full Cross-
Year Sample
Section Sample
Section 1980
0.038 0.039
0.038 0.039
1981 0.033
0.033 0.015
0.016 1982
0.039 0.037
0.014 0.011
1983 0.032
0.031 0.010
0.008 1984
0.041 0.043
0.015 0.016
1985 0.052
0.053 0.020
0.018 1986
0.070 0.068
0.024 0.022
1987 0.081
0.080 0.024
0.023 1988
0.090 0.091
0.028 0.029
1989 0.073
0.076 0.011
0.010 1990
0.089 0.088
0.019 0.018
1991 0.080
0.079 0.011
0.010 1992
0.082 0.081
0.014 0.015
1993 0.080
0.082 0.010
0.010 1994
0.093 0.096
0.015 0.013
1996 0.118
0.120 0.027
0.024 1998
0.130 0.131
0.030 0.028
2000 0.167
0.166 0.047
0.044 Number of observations
4,926 3,108
Notes: Attrition rates are dened as the number of noninterviews out of the women in the sample. Rates of rst attrition are dened as the number of women not interviewed in a given year out of the women
who have continuously remained in the sample throughout that year.
The descriptive statistics are grouped based on the year of observation. In the rst and fth columns the observations across all years 1986, 1988, 1990, 1992, 1994,
1996, 1998, and 2000 are pooled, in the second and sixth columns the observations from 1986, 1988, and 1990 are pooled, in the third and seventh columns those obser-
vations from 1992, 1994, and 1996 are pooled, and in the fourth and eight columns observations from 1998 and 2000 are pooled.
In both the full sample and the cross-section, the members of the continuous sub- sample have family incomes that are slightly larger than those for the entire sample,
implying that the distribution of family income for attritors lies below that of nonat- tritors. In each of the samples, however, the marital status of the women, the presence
of children, the incidence of poverty, and highest grade completed appear to be largely unaffected by the exclusion of the attritors. Table 2 shows that once the
NLSY79-C begins, the effects of attrition on the sample of women in the NLSY79 are small. However, this comparison neglects the women who permanently attrite
from the NLSY79 prior to the 1986 interview.
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All Annual Observations Annual observations, Continuous Subsample
All 1986,
1992, 1998
All 1986,
1992, 1998
Child 1988, and
1994, and and
Child 1988, and
1994, and and
Years 1990
1996 2000
Years 1990
1996 2000
Age Mean
32 27
33 38
32 27
33 38
Median 32
27 33
38 32
27 33
38 10 percent
25 23
29 35
25 23
29 35
90 percent 39
31 37
41 39
31 37
41 Any children
0.70 0.60
0.75 0.78
0.70 0.60
0.75 0.79
Number of children Mean
1.44 1.14
1.60 1.69
1.47 1.15
1.63 1.71
Median 1
1 2
2 1
1 2
2 10 percent
90 percent 3
3 3
3 3
3 3
3 Marital status
Never married 0.26
0.36 0.23
0.17 0.26
0.36 0.23
0.18 Married
0.54 0.50
0.56 0.58
0.55 0.50
0.57 0.59
Separated 0.06
0.05 0.07
0.07 0.06
0.05 0.07
0.06 Divorced
0.12 0.09
0.13 0.16
0.12 0.08
0.13 0.16
Widowed 0.02
0.00 0.01
0.03 0.01
0.01 0.00
0.01 Family income
Mean 29,790
23,277 34,607
32,970 30,153
23,697 34,475
33,599 Median
22,007 19,355
22,310 26,224
22,678 19,756
22,966 27,011
10 percent 5,437
5,139 5,577
6,002 5,790
5,323 6,063
6,603 90 percent
52,399 45,806
51,969 62,617
53,072 46,524
52,148 62,928
Poverty status 0.19
0.21 0.18
0.15 0.18
0.21 0.17
0.14 Highest grade completed
Mean 13
13 13
13 13
13 13
13 Median
12 12
12 12
12 12
12 12
10 percent 11
10 11
11 11
11 11
12 90 percent
16 16
16 16
16 16
16 16
Notes: “All child years” includes years 1986, 1988, 1990, 1992, 1994, 1996, 1998, and 2000. indicates that some observations are missing values for these variables.
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All Annual Observations Annual observations, Continuous Subsample
All 1986,
1992, 1998
All 1986,
1992, 1998
Child 1988, and
1994, and and
Child 1988, and
1994, and and
Years 1990
1996 2000
Years 1990
1996 2000
Age Mean
32 27
33 38
32 27
33 38
Median 32
27 33
38 32
27 33
38 10 percent
25 23
29 35
25 23
29 35
90 percent 39
31 37
41 39
31 37
41 Any children
0.67 0.55
0.73 0.77
0.68 0.56
0.74 0.78
Number of children Mean
1.33 1.01
1.49 1.60
1.37 1.03
1.52 1.63
Median 1
1 2
2 1
1 2
2 10 percent
90 percent 3
3 3
3 3
3 3
3 Marital status
Never married 0.22
0.31 0.17
0.13 0.21
0.31 0.17
0.12 Married
0.61 0.55
0.64 0.66
0.62 0.55
0.65 0.67
Separated 0.05
0.04 0.05
0.05 0.04
0.04 0.05
0.04 Divorced
0.12 0.09
0.13 0.16
0.12 0.09
0.13 0.15
Widowed 0.00
0.00 0.01
0.00 0.01
0.01 0.00
0.01 Family income
Mean 33,416
25,582 39,963
36,155 33,689
25,990 39,534
36,854 Median
24,913 21,774
25,744 29,841
25,543 22,305
26,247 30,612
10 percent 6,530
5,916 6,920
7,477 6,996
6,162 7,489
8,163 90 percent
55,701 48,387
55,363 65,541
56,055 49,257
55,433 65,660
Poverty status 0.14
0.16 0.13
0.11 0.13
0.15 0.11
0.11 Highest grade completed
Mean 13
13 13
13 13
13 13
14 Median
12 12
12 12
12 12
12 13
10 percent 11
11 12
12 12
11 12
12 90 percent
16 16
16 17
16 16
16 17
Notes: “All child years” includes years 1986, 1988, 1990, 1992, 1994, 1996, 1998, and 2000. indicates that some observations are missing values for these variables.
Next, I describe the attrition patterns for the children of the NLSY79 women. The samples of children examined in this paper are limited to children born in 1994 or
earlier so that the children will be old enough to have been assessed and to have had at least one chance to attrite after assessment. Because the children are no longer
eligible for assessment upon turning 15, they are dropped from the samples at age 15.
4
There are two difculties in examining the attrition patterns for the children. First, because children are being born into the sample as the survey continues causing the
sample to change over time, the patterns must be described separately for groups of children based on their year of birth. Second, some of the children who are, by deni-
tion, part of the sample have never been identied, much less assessed. For instance, there would be no information collected about a child born in 1991 whose mother
attrited in 1989 and never returned to the survey. Using information on fertility through the 2000 interview for those women who are interviewed in that round, the
expected number of missed births is approximately 150, with an upper bound of 330.
5
Table 3 shows the fraction of children about whom supplemental information was collected 1 out of the children known to have been born by the start of the interview
period and 2 out of the children whose mothers were interviewed. Because inter- viewers are instructed that interviewing the main youth is the highest priority, assess-
ing a child generally accompanies the collection of his mother’s interview. Conse- quently, having a mother who is interviewed substantially increases the odds that
information on the child is collected. There are few cases where the child assessment occurs, but the mother is not interviewed. Excluding the 2000 interview —at each
interview, supplemental information is not collected for 10 to 20 percent of all known children, and is missing for between 5 and 10 percent of the children whose mothers
are interviewed.
6
Table 4 attempts to assess the effects of attrition in the child supplement since its beginning in 1986. This table compares the descriptive statistics for the sample of all
child-year observations and the subsample of child-year observations for the chil- dren for whom supplemental information is collected in all eligible years the conti-
nuous subsample. This table is organized in the same way as Table 2. The statistics focus on the items that describe the child’s family background and the resources avail-
able to the child, such as, mother’s marital status, mother’s highest grade completed, average family income during the child’s rst three years, and maternal employment
during the child’s rst year, as well as, the child’s standard scores on the Peabody Pictorial Vocabulary Test PPVT and the Behavior Problems Index BPI.
For the full sample Table 4a and the cross-section Table 4b, the sample of all observation years and the continuous subsample are similar along the dimensions
presented. Although children in the continuous samples score higher on the PPVT,
4. Beginning in 1994, a young adult interview was conducted for those children 15 and older. The adminis- tration of the young adult interview is not linked to the interview of the mother.
5. The estimates of the number of children who are entirely omitted from the sample are calculated using information about the fertility of women who are interviewed in 2000. The mean number or the mean
plus one standard deviation of subsequent births for women of the same parity in the last survey that the attriting woman was interviewed is used as the number of missed births for each attriting woman.
6. Because of funding issues, a portion of the children were not eligible for interview in 2000. The ineligi- bles were randomly selected. In the 2002 interview, the entire sample of children was restored.
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1986 1988
1990 1992
1994 1996
1998 2000
Number of Mother
Mother Mother
Mother Mother
Mother Mother
Mother observations
All Interview
All Interview
All Interview
All Interview
All Interview
All Interview
All Interview
All Interview
Born Prior to 1986 Interview Period Full sample
4,533 0.90
0.95 0.88
0.95 0.83
0.89 0.83
0.88 0.83
0.89 0.77
0.85 0.80
0.89 —
— Cross-section
2,462 0.90
0.95 0.89
0.95 0.83
0.89 0.83
0.88 0.83
0.89 0.78
0.84 0.79
0.88 —
— Born After Start of 1986 Interview Period and Prior to Start of 1988 Interview Period
Full sample 1,199
— —
0.90 0.96
0.88 0.95
0.89 0.94
0.87 0.94
0.83 0.91
0.83 0.92
0.62 0.72
Cross-section 730
— —
0.90 0.97
0.89 0.95
0.89 0.95
0.88 0.95
0.83 0.92
0.82 0.91
0.72 0.85
Born After Start of 1988 Interview Period and Prior to Start of 1990 Interview Period Full sample
1,010 —
— —
— 0.90
0.95 0.91
0.95 0.89
0.95 0.84
0.92 0.84
0.91 0.65
0.74 Cross-section
638 —
— —
— 0.91
0.96 0.91
0.95 0.90
0.96 0.82
0.92 0.83
0.91 0.75
0.85 Born After Start of 1990 Interview Period and Prior to Start of 1992 Interview Period
Full sample 806
— —
— —
— —
0.92 0.95
0.92 0.96
0.87 0.93
0.85 0.92
0.66 0.74
Cross-section 520
— —
— —
— —
0.92 0.95
0.92 0.96
0.88 0.93
0.84 0.90
0.75 0.86
Born After Start of 1992 Interview Period and Prior to Start of 1994 Interview Period Full sample
779 —
— —
— —
— —
— 0.93
0.96 0.89
0.94 0.87
0.93 0.68
0.75 Cross-section
477 —
— —
— —
— —
— 0.94
0.97 0.90
0.95 0.87
0.94 0.80
0.87 Born After Start of 1994 Interview Period and Prior to Start of 1996 Interview Period
Full sample 481
— —
— —
— —
— —
— —
0.88 0.92
0.90 0.95
0.67 0.74
Cross-section 310
— —
— —
— —
— —
— —
0.89 0.93
0.92 0.97
0.76 0.84
Notes: In 2000, about 38 percent of the Black and Hispanic oversamples were not eligible for interview because of funding constraints. In calculating the fraction of children interviewed in 2000, the ineligible have been removed from the denominator. The ineligibles were randomly selected.
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Table 4a Descriptive Statistics for Person-Year Observations of Children, Children Born in 1994 or Earlier: Full Sample
All Annual Observations Annual observations, Continuous sample
All 1986,
1992, 1998
All 1986,
1992, 1998
Child 1988, and
1994, and and
Child 1988, and
1994, and and
Years 1990
1996 2000
Years 1990
1996 2000
Child’s age in months Mean
88 69
94 117
92 73
98 118
Median 87
63 94
120 92
68 101
120 10 percent
22 13
26 68
24 14
28 69
90 percent 155
131 159
163 158
137 162
164 Number of children in family
Mean 2.52
2.36 2.60
2.66 2.54
2.39 2.62
2.66 Median
2 2
2 2
2 2
2 2
10 percent 1
1 1
1 1
1 1
1 90 percent
4 4
4 4
4 4
4 4
Mother’s marital status Never married
0.16 0.21
0.14 0.10
0.16 0.21
0.14 0.10
Married 0.63
0.61 0.64
0.67 0.64
0.61 0.65
0.69 Separated
0.08 0.08
0.08 0.07
0.08 0.08
0.08 0.07
Divorced 0.12
0.10 0.12
0.14 0.11
0.10 0.12
0.14 Widowed
0.01 0.01
0.01 0.01
0.01 0.01
0.01 0.01
Mother’s highest grade Mean
12 12
13 13
13 12
13 13
Median 12
12 12
12 12
12 12
13 10 percent
10 9
10 11
10 9
10 12
90 percent 16
14 16
16 16
14 16
16
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Median 20,945
16,729 21,453
29,283 21,371
16,945 22,026
30,012 10 percent
5,459 4,919
5,706 7,297
5,692 5,076
6,035 7,868
90 percent 49,827
40,323 50,519
66,791 49,844
40,363 49,869
66,044 Hours worked in rst year
Mean 688
565 720
840 691
567 710
857 Median
62 132
463 105
144 520
10 percent 90 percent
2,080 1,880
2,080 2,080
2,080 1,894
2,80 2,080
Worked in rst year 0.51
0.46 0.53
0.58 0.52
0.47 0.53
0.59 Child’s PPVT score
Mean 89
85 90
94 90
86 91
95 Median
90 87
91 95
91 88
92 97
10 percent 64
60 67
68 65
61 68
70 90 percent
113 109
113 118
114 109
114 120
Child’s BPI score Mean
106 108
106 104
106 108
107 103
Median 105
107 105
103 106
107 106
103 10 percent
88 90
88 84
88 90
89 84
90 percent 126
126 126
123 125
126 126
122 Number of observations
39,607 15,125
17,673 6,809
28,902 10,941
12,653 5,308
Notes: “All child years” includes years 1986, 1988, 1990, 1992, 1994, 1996, 1998, and 2000. indicates that some observations are missing values for these variables. PPVT and BPI scores are standardized for age of the child.
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Table 4b Descriptive Statistics for Person-Year Observations of Children, Children Born in 1994 or Earlier: Cross-section
All Annual Observations Annual observations, Continuous sample
All 1986,
1992, 1998
All 1986,
1992, 1998
Child 1988, and
1994, and and
Child 1988, and
1994, and and
Years 1990
1996 2000
Years 1990
1996 2000
Child’s age in months Mean
86 65
90 116
88 67
92 116
Median 85
59 89
118 87
62 91
118 10 percent
21 11
24 68
22 12
24 67
90 percent 153
127 156
162 155
131 158
163 Number of children in family
Mean 2.41
2.26 2.47
2.54 2.43
2.29 2.48
2.54 Median
2 2
2 2
2 2
2 2
10 percent 1
1 1
1 1
1 1
1 90 percent
4 4
4 4
4 4
4 4
Mother’s marital status Never married
0.09 0.13
0.08 0.06
0.08 0.13
0.08 0.06
Married 0.73
0.70 0.74
0.75 0.74
0.71 0.75
0.76 Separated
0.06 0.06
0.06 0.06
0.05 0.06
0.05 0.05
Divorced 0.12
0.10 0.12
0.13 0.11
0.10 0.11
0.13 Widowed
0.01 0.01
0.01 0.01
0.01 0.01
0.01 0.01
Mother’s highest grade Mean
12 12
13 14
13 12
13 14
Median 12
12 12
12 12
12 12
13 10 percent
10 10
11 12
11 10
11 12
90 percent 16
15 16
16 16
15 16
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Mean 32,631
23,274 37,799
38,648 32,181
23,240 36,216
38,784 Median
24,930 20,446
25,949 33,013
25,234 20,968
26,057 33,206
10 percent 6,308
5,576 6,780
8,403 6,605
10,595 7,242
8,972 90 percent
53,772 43,306
54,740 67,098
53,084 42,831
53,287 66,231
Hours worked in rst year Mean
715 589
743 859
735 603
753 885
Median 221
282 560
285 15
332 626
10 percent 90 percent
2,080 1,920
2,080 2,080
2,080 1,950
2,080 2,080
Worked in rst year 0.54
0.49 0.56
0.60 0.56
0.50 0.57
0.62 Child’s PPVT score
Mean 95
91 95
98 95
92 96
99 Median
96 93
96 99
96 94
96 99
10 percent 71
67 74
76 72
68 73
77 90 percent
116 112
116 122
117 113
117 123
Child’s BPI score Mean
106 108
106 103
106 108
106 103
Median 105
107 105
102 105
108 105
102 10 percent
86 90
87 84
88 91
88 84
90 percent 124
126 124
121 124
126 124
121 Number of observations
23,585 8,489
10,575 4,521
18,419 6,359
8,232 3,828
Notes: “All child years” includes years 1986, 1988, 1990, 1992, 1994, 1996, 1998, and 2000. indicates that some observations are missing values for these variables. PPVT and BPI scores are standardized for age of the child.
Table 5 Means for Children’s Mothers 1979: All Known Children, and Children who
were Continuously, Sometimes, and Never in the Child Supplement
Continuously Sometimes in
Never in in NLSY79-C
NLSY79-C NLSY79-C
All Sample
Sample Sample
Full Sample Age
17.87 17.93
17.73 18.10
Any children 0.23
0.24 0.20
0.31 Number of children
0.33 0.35
0.27 0.49
Married 0.18
0.19 0.16
0.28 Divorced
0.01 0.01
0.01 0.01
Separated 0.02
0.02 0.02
0.04 Widowed
0.00 0.00
Never married 0.79
0.78 0.81
0.68 Highest grade completed
10.32 10.40
10.21 10.03
AFQT score 33.21
35.60 28.83
30.53 Number of observations
8,457 5,256
2,846 355
Cross-Section Age
17.89 17.91
17.81 18.01
Any children 0.19
0.19 0.19
0.25 Number of children
0.27 0.27
0.26 0.37
Married 0.19
0.19 0.18
0.30 Divorced
0.01 0.01
0.01 0.00
Separated 0.02
0.02 0.03
0.02 Widowed
Never married 0.78
0.78 0.78
0.67 Highest grade completed
10.54 10.61
10.41 10.23
AFQT score 41.79
44.11 36.36
39.36 Number of observations
4,950 3,322
1,424 204
Notes: Sample is composed mothers of children born in 1994 or earlier. indicates that some observations are missing values for these variables.
most characteristics of the children and their families are affected little by whether attritors are included or excluded. In general, the comparisons in Table 4 imply that
small differences exist between attritors and nonattritors. However, the comparisons neglect the group of children for whom supplemental information is never collected;
they are potentially different from those for whom supplemental information is col- lected at least once.
Table 5 explores the differences between mean 1979 characteristics of the mothers of the children who are and are not included in the child supplement. This information
is presented for all known children and three subsamples: 1 children continuously in the sample, 2 children for whom supplemental information is sometimes col-
lected, and 3 children for whom supplemental information is never collected. The comparisons are done separately for the full and cross-sectional samples. Although
the mothers of children in the continuous sample score higher on the AFQT than the mothers of children who are either sometimes or never in the NLSY-C, along most
other dimensions they look similar to the mothers of the children for whom supple- mental information is sometimes collected. The mothers of the children for whom
supplemental information is never collected look different in that they are the most likely to have had a child and the least likely to have never been married at the 1979
interview.
Overall, children who are surveyed in some of the child supplement years in which they are eligible are similar to those who are surveyed in all eligible years. The
mothers of these two groups of children also appear similar. However, the children who are not interviewed in any of the mother-child supplement years and their moth-
ers are different. These mothers more often experienced an early marriage or birth. Attrition from the NLSY79 prior to the start of the child supplement appears nonran-
dom with respect to women’s fertility through 1979 and marital status at that time. Evaluating the effects that this attrition has on the sample of children is made difcult
because there is no information on children whose mothers attrite before their births, but the fact that there are not many of these children minimizes the chance that their
absence will have large consequences.
III. Nature of Attrition
