The French paradox and other ecological fallacies

The Ecological Fallacy and the complexity of the appropriate weightings to apply for aggregated vs individual data, has recently been subjected to scrutiny in this journal. In 1981, three Frenchmen, Ducimetiere, Cambien and Richard, coined the term The French Paradox, after having compared levels of heart disease with fat intake data provided by The Organisation for Economic Cooperation and Development. Consumption of animal fat in France was high despite the fact that mortality data showed age-standardized male mortality rates (35–64 years of age) lying just above Greece and Japan. In fact, the classic risk factors did not explain the 4-fold gradient in ischaemic heart disease later observed between Toulouse and Belfast. Ecological Fallacies typically arise when disease differences identified between countries are assumed to be caused by factors that are found to also differ—in reality the differences may be due to unknown factors. The French Paradox is an unusual example in that it compares the large differences in ischaemic heart disease between France and other countries, finds that major risk factors do not differ, and infers that the differences must be caused by unknown factors. In any case, the comparison of heart disease between France and elsewhere is far from new. A difference in the prevalence of angina pectoris between Ireland and France had been noted by Samuel Black as early as 1819. It was William Heberden who coined the term Angina Pectoris, thereby drawing attention to the condition, in 1768. Black was born in 1763–64 near Dromore, County Down, attended Edinburgh University from 1782 to 1786, and graduated with an MD. He entered practice in Newry, County Down in 1788 and published the first of four cases of angina pectoris in 1795; he died in 1832. In his book Clinical and Pathological Reports published in Newry in 1819 it appeared to him ‘that the Physician who ascertains half a dozen of important facts, performs a more valuable, though a less splendid achievement, than he who invents a dazzling theory’. Yet, Black did truly help develop a dazzling theory—the ischaemic hypothesis of angina pectoris. A most remarkable feature of Black’s work was that he adopted an epidemiological stance in asking how individuals with angina pectoris differed from those without it. He put it more eloquently: ‘Is our knowledge of the remote causes of this disease such as to enable us to classify the liable and the exempt?’ He feared not, but continued: