Income and IQ in the NLSY79

The 1979 cohort of the National Longitudinal Survey of Youth (NLSY79) tracks a representative group of Americans born between 1958 and 1964. The NLSY79 includes an oversample of black and Hispanic Americans as well as a military sample. These extra samples were not included in this analysis.

Income

Income was defined as a participant’s average annual income from wages and businesses profits over the years where they were between the age of 36 and 42.

IQ

Almost all participants of the NLSY79 took the Armed Forces Qualification Test (AFQT) between the ages of 16 and 22. The AFQT is used here as a proxy for IQ and its score is given as a percentile; for instance, a score of 75 indicates performance better than 75% of test-takers.

I considered correcting participants’ AFQT scores for the age at which they took it, but opted not to as I only found a correlation of 0.005 between birth year and AFQT score.

Results

Among men a correlation of 0.4 was observed.

Splitting the data between above and belong average IQ we see that the strength of the relationship is roughly the same on both ends. Below the 50th percentile we have a correlation of 0.29 and below it we have a correlation of 0.25.

With men and women together the correlation 0.35.