Bell Curve

5 74 Appendix 2 Appendix 2 575and occupation. Since the purpose of the index was to measure the socioeconomicenvironment in which the NLSY ~outh was raised, thespecific variables employed referred to the parents' status: total net familyincome, mother's education, father's education, and an index of occupationalstatus of the adults living with the subject at the age of 14.The population for the computation was limited to the 11,878 NLSYsubjects with valid AFQT scores. In more detail:Mother's education and father's education were based on years of education,converted to standardized scores.Family income was based on the averaged total net family income for1978 and 1979, in constant dollars, when figures for both years wereavailable. If income for only one of the two years was reported, that yearwas used. Family income was excluded if the subject was a Schedule Cinterviewee (the reported income for the year in question referred to hisor her own income, not to the parental household's income). The dollarfigure was expressed as a logarithm before being standardized. Thisprocedure, customary when working with income data, has the effect ofdiscounting extremely high values of income and permitting greater discriminationamong lower incomes. A minimum standardized value of-4 was set for incomes of less than $1,000 (all figures are in 1990dollars).Parental occupation was coded with a modified version of the Duncansocioeconomic index, grouping the Duncan values (which go from1 to 100) into deciles. A value of -1 was assigned to persons out of thelabor force altogether. It was assumed that the family's socioeconomicstatus is predominantly determined by the higher of the two occupationsheld by two parents. Thus the occupational variable was based onthe higher of the two ratings of the two parents. The increment in socioeconomicstatus represented by both parents holding high-status occupationsis indirectly reflected in the higher income and in the twoeducational variables. The eleven values in the modified Duncan scalewere standardized.The reliability of the four-indicator index (Cronbach's a) is .76. Thecorrelations among the components of the index are shown in the table.The four variables were summed and averaged. If only a subset of variableshad valid scores, that subset was summed and averaged. By far themost common missing variable was family income, since many of theNLSY youths were already living in independent households as ofCorrelations of Indicators in theSocioeconomic Status IndexMother's Father's ParentalEducation Education OccupationFather's education .63 -Parental occupation .47 .55 -Family income .36 .40 .47the beginning of the survey, and hence were reporting their ownincome, not parental income. Overall, data were available on all fourindicators for 7,447 subjects, for three on an additional 3,612, on twofor 679, and on one for 138. Two subjects with valid scores on the AFQThad no information available on any of the four indicators. For use inthe regression analyses, the SES index scores were set to a mean of 0and a standard deviation of 1.EDUCATIONAL ATTAINMENTHighest G rd Completed.The NLSY creates a variable each year for "highest grade completed,"incorporating information from several questions.7 For analyses basedon the occurrence of an event (e.g., the birth of a child), the value of"highest grade completed" for the contemporaneous survey year is used.For all other analyses, the 1990 value for "highest grade completed" isused. Values run from 0 through 20.Highest Degree Ever ReceivedIn the 1988-1990 surveys, the NLSY asked respondents to report thehighest degree they had ever received. The possible responses were: highschool diploma, associate degree, bachelor of arts, bachelor of science,master's, Ph.D., professional degree (law, medicine, dentistry), and"other." These self-reported degrees were sometimesespeciallywhen the degree did not correspond to the number of years ofeducation (e.g., a bachelor's degree for someone who also reported onlyfourteen years of education). To eliminate the most egregiously suspi-