• Child health
• health behaviour
• radiation

Divan et al1 find that prenatal and postnatal exposure to cell phone use is associated with behavioural problems at age 7 years. The study controls for relevant confounders, but the results nevertheless indicate that unobserved heterogeneity is present, I argue. What particularly draws my attention is the declining effect of prenatal and postnatal cell phone use on behavioural problems for the birth years between 1998 and 2000 (see tables 1 and 2 in Divan …