Science

Psychologists have found that two common questionnaires for assessing depression don’t work for comparing people of differing intelligence—and the problem may extend to other conditions and traits.

For a recent study in the journal Intelligence, Stanisław Czerwiński of the University of Gdańsk in Poland and his colleagues investigated how intelligence correlates with mental health. They hypothesized that the association between intelligence and better mental health starts out positive as it approaches the high end of the IQ scale, then turns negative.

The data revealed the curved relation the researchers were expecting: the highest intelligence levels seemed to be associated with declines in mental health. But then the scientists found a problem. To make sure their results were valid, they ran statistics tests to determine whether the mental health measures work the same for people at different intelligence levels, in part by calculating whether responses to individual questions reflect depression to the same extent for everybody. Both scales failed this test, meaning they can’t be used to compare people with differing intelligence—and conclusions like this study’s can’t be trusted.