• PSYCHOLOGY

In a recent paper, Messerli1 reported a strong positive association between national chocolate consumption and the number of Nobel prizes a country has won. If this association had occurred at the level of individual people, then the conclusions would have been remarkable, and academics around the world would doubtless be ordering chocolate by the tonne in an attempt to realise their lifelong dreams. His analysis, however, was what epidemiologists call an ecological analysis. Data were aggregated by country, and so the results suggested that countries with high chocolate consumption have tended to produce many Nobel prize winners; crucially, however, we do not know what were the eating habits of the prize winners themselves. Ecological studies are generally regarded as hypothesis-generating; those of us who try to teach the basics of epidemiology to medical students warn them of possible dangers by urging them to …