Pooling Sample Sizes

Pooling Sample Sizes

The panel dimension of the NLSY79 data collection permits one to cumulate sample cases for children at specified ages across survey points, thus attaining rather substantial sample sizes for those ages. Pooling in this manner also can greatly enhance the heterogeneity of the sample for specific research topics. The trade-off to this methodology is that the ability to follow a particular age cohort across survey years becomes somewhat limited, although it is still doable for selected research topics. Table 1 below highlights potential sample sizes using this approach.

Pooling the Child samples. From the perspective of the younger children, it is possible to attain single year of age samples numbering in the thousands for specific research efforts. For example, if one wishes to examine associations between scores on the digit span assessment and other factors for seven year olds, it would be possible to cumulate a sample of about 4,000 seven-year-old children from the first to the current assessment survey year (see Table 1 below). Because these children would have been born to mothers in all years between 1979 and the current survey round (see Table 2 in the Sample Design section), the mothers of these children would range in age from their teens to their forties. The relevance of this pooling approach for evaluation of the child data, utilizing various assessments, is dealt with in the "Repeat Assessments" section of the Child Assessments--Introduction.

Pooling the Young Adults. Parallel estimates can be found for young adults. Because the young adult interviews have only been ongoing since the 1994 survey round, no single year-of-age cumulative estimate can include more than eleven points. Nonetheless, returning to Table 1 below, the number of cases cumulated in this way for ages 15 to 18 all attain single year of age totals of between 3,417 and 3,560 cases. It is worth noting that this sample cumulation modestly increases the heterogeneity of these young adult samples. For example, cumulating cases at these early young adult ages expands the age of the mothers at children's birth from mid-adolescence to the late forties. Because beginning in 2010 young adults age 31-32, 35-36, 39-40, 43-44, etc., as of December 31 of the survey year are not fielded, pooled sample sizes in these age ranges will be constrained.

Table 1. NLSY79 Child and Young Adult Sample Types for Pooled Age Groups through the Current Survey Round

Younger Children
Pooled Age Groups 1986-2016 Survey Round
Total Possible # Males Females
0 year olds 2704  1412 1292
1 year olds 3102 1586 1516
2 year olds 3281 1654 1627
3 year olds 3537 1799 1738
4 year olds 3698 1878 1820
5 year olds 3875 1989 1886
6 year olds 3911 1999 1912
7 year olds 4042 2058 1984
8 year olds 4085 2057 2028
9 year olds 4068 2059 2009
10 year olds 4146 2097 2049
11 year olds 4062 2062 2000
12 year olds1 4037 2056 1981
13 year olds2 3997 2041 1956
14 year olds3 2267 1145 1122
 
Young Adult Children
Pooled Age Groups 1994-2016 Survey Round
Total Possible # Males Females
14 Year Olds 1904 975 929
15 Year Olds 3417 1747 1670
16 Year Olds 3540 1829 1711
17 Year Olds 3395 1699 1696
18 Year Olds 3560 1789 1771
19 Year Olds 3301 1621 1680
20 Year Olds 3391 1698 1693
21 Year Olds 3183 1550 1633
22 Year Olds 3054 1525 1529
23 Year Olds 2934 1433 1501
24 Year Olds 2919 1408 1511
25 Year Olds 2703 1352 1351
26 Year Olds 2568 1205 1363
27 Year Olds 2404 1212 1192
28 Year Olds 2232 1081 1151
29 Year Olds 1974 967 1007
30 Year Olds 1507 695 812
31 Year Olds 429 206 223
32 Year Olds 419 171 248
33 Year Olds 1055 505 550
34 Year Olds 955 458 497
35 Year Olds 202 96 106
36 Year Olds 88 41 47
37 Year Olds 434 197 237
38 Year Olds 368 184 184
39 Year Olds 81 33 48
40 Year Olds 16 5 11
41 Year Olds 78 36 42
42 Year Olds 60 28 32
43 Year Olds  6  3 3
44 Year Olds 1  0 1
45 Year Olds 1  0 1
46 Year Olds 1  0  1
       

NOTE: Ages are computed as of survey dates. For the Younger Children portion of this table, the counts are cumulative from 1986 to the current interview and are based on a child being interviewed in at least one survey year. In 2016, the Mother Supplement remained in the NLSY79 questionnaire, but the Child Supplement was not administered. Starting in 1994, children who turned 15 or older as of December 31st of the reference year of the survey round were fielded as Young Adults. Some were age 14 when interviewed. Beginning in 2016, the inclusions age for the Young Adult fielding was lowered to 12. Those turning 14 went through the traditional YA survey, but those turning 12 or 13 answered far fewer questions, primarily drawn from the Child Supplement. The Young Adult Children portion of this table includes only those children aged 14 or older who have completed at least one Young Adult survey from 1994 to the current interview. Users should note that beginning in 2010 young adults age 31-32, 35-36, 39-40, 43-44, etc, as of December 31 of the survey year are not fielded; thus, pooled sample sizes in these age ranges will be constrained.

1 Of the 21 12 year olds in R27, 20 have both Mother Supplement and YA interview data.

2 Of the 28 13 year olds in R27, 26 have both Mother Supplement and YA interview data.

3 Beginning in 2012, the NLSY79 field period routinely crossed into the year after the reference year for fielding in the Child versus Young Adult samples. Subsequently, some of the 14 year olds had turned 15 by the point of their actual interview.