Bell Curve

118 Cognitive Classes and Social Behavior Cognitive Chses and Social Behavior 1 19or poverty? Only a scattering of economists have broached the possibility.'This neglect points to a gaping hole in the state of knowledge aboutsocial behavior. It is not that cognitive ability has been considered andfound inconsequential but that it has barely been considered at all. Thechapters in, Part 11 add cognitive ability to the mix of variables that socialscientists have traditionally used, clearing away some of the mysterythat has surrounded the nation's most serious social problems.We will also argue that cognitive ability is an important factor inthinking about the nature of the present problems, whether or not cognitiveability is a cause. For example, if many of the single women whohave babies also have low IQ, it makes no difference (in one sense)whether the low IQ caused them to have the babies or whether the pathof causation takes a more winding route. The reality that less intelligentwomen have most of the out-of-wedlock babies affects and constrainspublic policy, whatever the path of causation. The simple correlation,unadjusted for other factors-what social scientists called the zero-ordercorrelation-between cognitive ability and social behaviors is sociallyimportant.The chapters of Part I1 cover a wide range of topics, each requiringextensive documentation. Many statistics, many tables and graphs,many citations to technical journals crowd the pages. But the chaptersgenerally follow a similar pattern, and many of the complexities willbe less daunting if you understand three basics: the NLSY, our use ofcognitive classes, and our standard operating procedure for statisticalanalysis.THE NLSYIn Part 1, we occasionally made use of the National Longitudinal Surveyof Youth, the NLSY. In the chapters that follow, it will play the centralrole in the analysis, with other studies called in as available andappropriate.Until a few years ago, there were no answers to many of the questionswe will ask, or only very murky answers. No one knew what the relationshipof cognitive ability to illegitimacy might be, or even the relationshipof cognitive ability to poverty. Despite the millions of mentaltests that have been given, very few of the systematic surveys, and sometimesnone, gave the analyst a way to conclude with any confidence thatthis is how IQ interacts with behavior X for a representative sample ofAmericans.Several modem sources of data have begun to answer such questions.The TALENT database, the huge national sample of high school studentstaken in 1961, is the most venerable of the sources, but its followupsurveys have been limited in the range and continuity of their data.The Panel Study of Income Dynamics, begun in 1968 and the nation'slongest-running longitudinal database, administered a brief vocabularytest in 1972 to part of its sample, but the scores allow only rough discriminationsamong people in the lower portions of the distribution ofintelligence. The National Longitudinal Survey begun by the Departmentof Education in 1972 (not to be confused with the NLSY) providesanswers to many questions associated with educational outcomes.The department's more ambitious study, High School and Beyond, conductedin the early 1980s, is also useful.But the mother lode for scholars who wish to understand the relationshipof cognitive ability to social and economic outcomes is theNLSY, whose official name is the National Longitudinal Survey of LaborMarket Experience of Youth. When the study began in 1979, theparticipants in the study were aged 14 to 22.13' There were originally12,686 of them, chosen to provide adequate sample sizes for analyzingcrucial groups (for example, by oversampling blacks, Latinos, and lowincomewhites), and also incorporating a weighting system so thatanalysts could determine the correct estimates for nationally representativesamples of their age group. Sample attrition has been kept lowand the quality of the data, gathered by the National Opinion ResearchCouncil under the supervision of the Center for Human Resources Researchat Ohio State University, has been excellent.The NLSY is unique because it combines in one database all the elementsthat hitherto had to be studied piecemeal. Only the NLSY combineddetailed information on the childhood environment and parentalsocioeconomic status and subsequent educational and occupationalachievement and work history and family formation and-crucially forour interestdetailed psychometric measures of cognitive skills.The NLSY acquired its cognitive measures by a lucky coincidence.In 1980, a year after the first wave of data collection, the Departmentof Defense decided to update the national norms for its battery of enlistmenttests. At the time, it was still using test scores from World WarI1 recruits as the reference population. Because the NLSY had just gone