INDEPENDENCE

This statistic of 1 in 73 million came from the Confidential Enquiry for Still- births and Deaths in Infancy (CESDI), an authoritative and detailed study of deaths of babies in five regions of England between 1993 and 1996. There it is estimated that the chances of a randomly chosen baby dying a cot death are 1 in 1,303. If the child is from an affluent, nonsmoking family, with the mother over 26, the odds fall to around 1 in 8,500. The authors go on to say that if there is no link between cot deaths of siblings (because we have eliminated the biggest known and possibly shared factors influencing cot death rates) then we would be able to estimate the chances of two children from such a family both suffering a cot death by squaring 1/8,500—giving 1 chance in 73 million.

So far so good. But are cot deaths in the same family really independent? The website for the Foundation for the Study of Infant Death (FSID) says baldly that “second cot deaths in the same family are very rare.“ This is no help, because so are first-sibling cot deaths—what we need to know is, how comparatively rare? Does having one child die a cot death increase the chances that you will have another do so?

Ray Hill . . . estimates that siblings of children who die of cot death are be- tween 10 and 22 times more likely than average to die the same way. Using the figure of 1 in 1,303 for the chance of a first cot death, we see that the chances of a second cot death in the same family are somewhere between 1 in 60 and 1 in 130. There isn’t enough data to be more precise, or to take familial factors into account, but it seems reasonable to use a ballpark figure of 1 in 100. Multiply- ing 1/1,303 by 1/100 gives an estimate for the incidence of double cot death of around 1 in 130,000. . . .