Title: Intelligence and family size reconsidered.

POPLINE Document Number: 035918

Author(s):

Retherford RD
Sewell WH

Source citation:

Honolulu, Hawaii, East-West Center, East-West Population Institute, 1986. 58, [12] p. (East-West Population Institute. Working Papers: a Prepublication Series Reporting on Research in Progress, No. 39.)

Abstract:

This report examines the measured intelligence (IQ) and subsequent fertility of over 9000 1957 Wisconsin high school graduates. Intelligence data come from high school IQ tests (as part of the Wisconsin Longitudinal Study (WLS) and fertility data come from 1975 interviews when most respondents were age 36. The report 1) reviews the related literature; 2) examines IQ and number of children born alive; 3) estimates the mean IQ, fertility, and mortality of high school dropouts; 4) uses IQ, fertility, and mortality estimates of both graduates and dropouts to estimate the IQ selection differential for the complete cohort; and 5) discusses the mean genotypic IQ generational change for the Wisconsin cohort. The relationship between IQ and fertility is negative for both sexes, but much more so for females who achieve the highest fertility in the second IQ decile (82-87). Males have less predictable fertility patterns. Both males and females have the lowest fertility in the 10th or highest decile (121-145). Data on high school dropouts comes largely from the 1960 census. The total fertility rate (TFR) for female dropouts is 3/4 of a child higher than for male dropouts, and is considerably higher than the TFR for female graduates; the TFR is only slightly higher for male dropouts than for graduates. Estimates of dropout IQs show males 1.09 standard deviations below that of graduates, and females 0.95 below graduates. Girls often drop out, not for academic reasons but because of pregnancy, thus accounting for little IQ difference between male and female dropouts, and higher TFRs for females than males. The data do not allow an estimation of generational change in genotypic IQ, but the authors think that it is a 3/8 of a point decline. Since this report's findings that mean IQ may be declining differ from studies that claim mean IQ is increasing, larger, longitudinal studies that compare parents' with childrens' IQs are needed.

Keywords:

Wisconsin
United States
North America
Intelligence
Personality
Family Size
Family Characteristics
Family and Household
Secondary Schools
Total Fertility Rate
Americas
Developed Countries
Psychological Factors
Behavior
Schools
Education
Fertility Rate
Birth Rate
Fertility Measurements
Fertility
Population Dynamics
Demographic Factors
Population