 42. Some Contributions of Economics to the Study of Personality 857
thus influence scores on IQ tests. Studies 
conducted over the past 40 years show that 
incentives can increase IQ scores, particu -
larly among low-IQ individuals. Providing 
M&M candies for correct answers can in -
crease scores by an amount equivalent to the 
Black–White gap in IQ.27 However, there 
is no evidence that the effect of incentives 
persists. It has yet to be shown that creat -
ing incentives for performance on one test 
improves performance on subsequent tests 
even of the same nature, or in any other life 
task. Indeed, there is some evidence that 
such incentives, in fact, may worsen sub -
sequent performance (Deci & Ryan, 1985; 
Ryan & Deci, 2000).
Not all persons respond with equal 
strength to incentives. Research by Borghans 
et al. (2008) and Segal (2012) shows that the 
responsiveness of persons to incentives on 
IQ and achievement tests depends on their 
noncognitive skills. Borghans et al. (2008) 
survey a body of literature that establishes 
the power of incentives to shape IQ scores. 
Duckworth, Quinn, Lynam, Loeber, and 
Stouthamer-  Loeber (2011) show that the 
motivation of test takers predicts IQ scores.
The same issues apply to measures of non -
cognitive skills. While less is known about the 
degree to which situations or incentives can 
affect how people respond to self-  reported 
measures of noncognitive skills, Chen, Feng, 
Heckman, and Kautz (2020) provide some 
experimental evidence. They conducted two experiments that show how survey 
conditions—  part of a student’s situation— 
can affect student responses on the Big Five 
questionnaire. The first experiment shows 
that providing information about the Big 
Five affects how students report on their 
skills. The second experiment shows that 
providing incentives for performance on a 
separate task affects how students respond 
on a Big Five questionnaire. This evidence 
demonstrates the need to standardize for 
aspects of the situation and incentives when 
measuring noncognitive skills.
The recent literature shows that noncog -
nitive skills predict standardized achieve -
ment test scores, which some psychologists 
assume are good measures of intelligence.28 
Figure 42.2  (based on Dutch data) shows 
how the variability across persons in the 
scores on one achievement test, the Differen -
tial Aptitudes Test (DAT),29 are determined 
by IQ and noncognitive measures. Noncog -
nitive skills explain a substantial portion of 
the variability across persons in DAT scores, 
as well as the variance in achievement scores 
above and beyond the variance that IQ ex -
plains when both measures of noncognitive 
skill and IQ are included in a regression. 
These findings caution the interpretation 
that standardized achievement tests only 
measure cognitive ability. They also capture 
noncognitive skills.30
In The Bell Curve, Herrnstein and Mur -
ray (1994) argued that intelligence is a pri -
FIGURE 42.2.  Decomposing variance explained for achievement tests and grades into IQ and noncogni -
tive skills: Stella Maris Secondary School, Maastricht, Holland. Source: Borghans et al. (2011a). Note: 
Grit is a measure of persistence on tasks (Duckworth et al., 2007).
