Complex comparisons

Thought on Low National IQs, Intellectual Disability, and Data Quality by Russell T. Warne.

I believe IQ measurements are demonstrably and reliably useful predictors of specified outcomes at a population level. I become much more leery about inter-country comparisons, not because of a distrust in the utility of IQ but a distrust in the reliability and meaningfulness of measurement on a global scale where you are dealing with all the nuance of language and culture.

Warne's piece is an affirmation of the importance of IQ but he has a good explication about the specific issues attached to doing cross-cultural, cross country comparisons.

Here is one dimension I do not see addressed very frquently.

However, the low estimated IQs for these countries do not imply that the majority (or even large percentages) of residents in these countries have an intellectual disability. That is because low IQ is not the sole diagnostic feature of an intellectual disability. According to the DSM-5:

The essential features of intellectual disability (intellectual developmental disorder) are deficits in general mental abilities (Criterion A) and impairment in everyday adaptive functioning, in comparison to an individual’s age-, gender-, and socioculturally matched peers (Criterion B). Onset is during the developmental period (Criterion C). The diagnosis of intellectual disability is based on both clinical assessment and standardized testing of intellectual and adaptive functions

American Psychiatric Association (2013, p. 37)

All three of these criteria must be met for a person to be diagnosed with an intellectual disability. Without any one of them, then a clinician should not diagnose a person with an intellectual disability.

Of these three criteria for diagnosis, an intelligence test can only provide evidence regarding Criterion A. The other two criteria require data about the presence and nature of functional impairments and a person’s developmental history. Intelligence tests do not provide this information (nor do test creators claim that they do).

People can have a low IQ score for a variety of reasons that have nothing to do with their actual intelligence (such as language barriers, low motivation, and malingering). For this reason, mental health professionals do not diagnose people with an intellectual disability solely on the basis of a low IQ. Indeed, because a person must perform lower than their “socioculturally matched peers” to have an intellectual disability, then by definition it is impossible for a majority (or even a substantially large minority) of people in a society to have an intellectual disability.

It is not possible to diagnose someone with an intellectual disability, let alone large numbers of people in a country, without examining how well they function in their day-to-day living. The inference that a low average national IQ indicates that many people have an intellectual disability is not supported.