Driving deprives your intelligence?

A surprising result of a study regarding driving and intelligence was announced recently in the UK.

Kishan Bakrania, a medical epidemiologist at the University of Leicester, explained the date he obtained suggesting that people with driving habit more than two hours in a day are likely to drop their cognitive function. According to the media, this survey investigated 93,000 people aged from 37 to 73 for five years. Participants who regularly drive a car for two or three hours in a day had lower IQ than those without or with little hours of driving. Also, they declined the IQ score more rapidly.

Independent: Driving for more than two hours a day makes you less intelligent, study finds

The researchers claimed that driving is an inactive behavior for your brain for an explanation of this result. Furthermore, they said to have found that use of a computer and gaming have a protective effect on your intelligence.

Unfortunately, I could not find the protocol of this cohort study on the online registry of clinical trials in the UK. Therefore, I cannot judge the validity of this study itself.

In my impression, this result is quite doubtful. At least, I will never trust this outcome unless this study is published in an academic journal with a good peer-review system. The causal relationship is not so easy to be proven in a mega-cohort.

An alternative explanation for this result is reverse causality. People with lower intelligence, perhaps with a tendency to decline, are likely to get a job for low income, typically driving jobs. Thus, their decline is not because they drive a car frequently. The researcher should comment this possibility.

In addition, examination of cognitive function is not so simple. This study is a cohort with large sample size. It is likely that a few simple tasks were adopted to measure their intelligence. Some cognitive tasks require examinee's dexterity. Others demand knowledge. It is difficult to evaluate a person's intelligence exactly with limited time.

I am worrying that several media reported this result sensationally. If the quality of this study does not match today's standard, vehicle drivers will get angry.