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 children at specific 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 2005 (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 on-going since the 1994 survey round, no single year-of-age cumulative estimate can include more than ten 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 3,298 and 3,273 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 thirties.

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

Younger Children
Pooled Age Groups 1986-Current Round
Total Possible # Males Females
0 year olds 2704  1412 1292
1 year olds 3102 1586 1516
2 year olds 3280 1653 1627
3 year olds 3535 1799 1736
4 year olds 3696 1876 1820
5 year olds 3872 1988 1884
6 year olds 3907 1997 1910
7 year olds 4035 2056 1979
8 year olds 4072 2050 2022
9 year olds 4050 2049 2001
10 year olds 4112 2074 2038
11 year olds 4013 2031 1982
12 year olds 3963 2012 1951
13 year olds 3904 1990 1914
14 year olds 2144 1086 1058
 
Young Adult Children
Pooled Age Groups 1994-Current Survey Round
Total Possible # Males Females
14 Year Olds 1862 955 907
15 Year Olds 3298 1684 1614
16 Year Olds 3351 1740 1611
17 Year Olds 3146 1569 1577
18 Year Olds 3273 1666 1607
19 Year Olds 2962 1459 1503
20 Year Olds 2986 1496 1490
21 Year Olds 2677 1299 1378
22 Year Olds 2563 1261 1302
23 Year Olds 2349 1147 1202
24 Year Olds 2289 1094 1195
25 Year Olds 2004 1006 998
26 Year Olds 1872 864 1008
27 Year Olds 806 820 1626
28 Year Olds 1480 716 764
29 Year Olds 1186 573 613
30 Year Olds 763 358 405
31 Year Olds 246 127 119
32 Year Olds 323 144 179
33 Year Olds 441 224 217
34 Year Olds 73 39 34
35 Year Olds 35 17 18
36 Year Olds 37 22 15
37 Year Olds 80 40 40
38 Year Olds 40 22 18
39 Year Olds 2 0 2
40 Year Olds 0 0 0
41 Year Olds 2 0 2
       
NOTE: Ages are computed as of survey dates.  For younger children, the counts are cumulative from 1986 to the current interview and are based on a child being interviewed in at least one survey year.  Young adults are counted if they have been interviewed, from 1994 to the current interview, in at least one year. Starting in 1994, children who are 14 at the survey date but who would reach age 15 by the end of the survey year are eligible for the Young Adult survey and are thus counted as young adults. Children, who were age 15 or older in any of the survey years prior to 1994, are not represented in this table unless they were interviewed as young adults from 1994 to the present.