Measurement confounding affects the extent to which verbal IQ explains social gradients in mortality

Assessing harmonized intelligence measures in a multinational study

Studies examining the neurocognitive and circuit-based etiology of psychiatric illness are moving toward inclusive, global designs. A potential confounding effect of these associations is general intelligence; however, an internationally validated, harmonized intelligence quotient (IQ) measure is not available. We describe the procedures used to measure IQ across a five-site, multinational study and demonstrate the harmonized measure's cross-site validity. Culturally appropriate intelligence measures were selected: four short-form Wechsler intelligence tests (Brazil, Netherlands, South Africa, United States) and the Binet Kamat (India). Analyses included IQ scores from 255 healthy participants (age 18-50; 42% male). Regression analyses tested between-site differences in IQ scores, as well as expected associations with sociodemographic factors (sex, socioeconomic status, education) to assess validity. Harmonization (e.g., a priori selection of tests) yielded the compatibility of IQ measures. Higher IQ was associated with higher socioeconomic status, suggesting good convergent validity. No association was found between sex and IQ at any site, suggesting good discriminant validity. Associations between higher IQ and higher years of education were found at all sites except the United States. Harmonized IQ scores provide a measure of IQ with evidence of good validity that can be used in neurocognitive and circuit-based studies to control for intelligence across global sites.

High school personality traits and 48-year all-cause mortality risk: results from a national sample of 26 845 baby boomers

Background

It is unclear if adolescent personality predicts mortality into late life, independent of adolescent socioeconomic status (SES).

Methods

Over 26 000 members of Project Talent, a US population cohort of high school students, completed a survey including 10 personality scales and SES in 1960. Multi-source mortality follow-up obtained vital status data through an average 48-year period ending in 2009. Cox proportional hazard models examined the relative risk associated with personality traits, as well as confounding by both a measure of SES and by race/ethnicity.

Results

Adjusted for sex and grade, higher levels of vigour, calm, culture, maturity and social sensitivity in high school were associated with reduced mortality risk (HRs=0.92 to. 96), while higher levels of impulsivity were associated with greater mortality risk. Further adjustment for SES and school racial/ethnic composition mildly attenuated (eg, 12%), but did not eliminate these associations. Final HRs for a 1 SD change in personality traits were similar to that for a 1 SD change in SES.

Conclusions

Adaptive personality traits in high school are associated with all-cause mortality in the USA as far into the future as the seventh decade, and to a degree similar to high school socioeconomic disadvantage.

The Intergenerational Transfer of Education Credentials and Health: Evidence from the 2008 General Social Survey-National Death Index

BACKGROUND

The educational attainment of a parent is a powerful predictor of children's wellbeing, but little is known about why this is the case.

METHODS

We used the 2008 General Social Survey to explore factors that may explain the relationship between one's father's education and one's own mortality. These include (1) intellectual traits, (2) material wellbeing, (3) psychological characteristics, (4) personality characteristics, and (5) social capital.

RESULTS

The education credentials of one's father are significantly associated with one's risk of death. The strongest mediators are own educational attainment, family income, home ownership, and subjective socioeconomic status. To a lesser extent, respondents' happiness with friends and family and social bonding were also pathways.

CONCLUSIONS

A father's educational attainment appears to influence his children's health, and may do so not only by improving the child's material circumstances but also through his or her educational attainment and other psychological and social characteristics.

Measurement confounding affects the extent to which verbal IQ explains social gradients in mortality

BACKGROUND

IQ is thought to explain social gradients in mortality. IQ scores are based roughly equally on Verbal IQ (VIQ) and Performance IQ tests. VIQ tests, however, are suspected to confound true verbal ability with socioeconomic status (SES), raising the possibility that associations between SES and IQ scores might be overestimated. We examined, first, whether two of the most common types of VIQ tests exhibited differential item functioning (DIF) favouring persons of higher SES and/or majority race/ethnicity. Second, we assessed what impact, if any, this had on estimates of the extent to which VIQ explains social gradients in mortality.

METHODS

Data from the General Social Survey-National Death Index cohort, a US population representative dataset, was used. Item response theory models queried social-factor DIF on the Thorndike Verbal Intelligence Scale and Wechsler Adult Intelligence Scales, Revised Similarities test. Cox models examined mortality associations among SES and VIQ scores corrected and uncorrected for DIF.

RESULTS

When uncorrected for DIF, VIQ was correlated with income, education, occupational prestige and race, with correlation coefficients ranging between |0.12| and |0.43|. After correcting for DIF, correlations ranged from |0.06| to |0.16|. Uncorrected VIQ scores explained 11-40% of the Relative Index of Inequalities in mortality for social factors, while DIF-corrected scores explained 2-29%.

CONCLUSIONS

Two of the common forms of VIQ tests appear confound verbal intelligence with SES. Since these tests appear in most IQ batteries, circumspection may be warranted in estimating the amount of social inequalities in mortality attributable to IQ.