Cohort studies have taught us everything we know. Well, not quite, but working my way through Helen Pearson’s The Life Project, it started to feel that way.
The relationship between smoking and low birth weight, between smoking and cancer, or even that pollutants you’re exposed to during childhood can cause serious diseases in later life – these are things we just know, right?
But according to this book, the key to this knowledge – and so much more – began with one over-ambitious maternity survey of every baby born in a single week in 1946, and persisted for several decades, due in large part to the single-minded determination of a doctor and an education expert.
Having grown up with a mother who loved to tell tea-time tales about milkmaids and cowpox revealing the secret of vaccination; or cholera-spreading standpipes mating with street maps to give birth to epidemiology, I was surprised to read the argument for cohort studies as the 20th-century’s equivalent. They must have been too contemporary to my mother’s 1960s education at Liverpool school of medicine, to have yet entered into the realm of lore.
Perhaps these are the stories today’s junior doctors are telling their children, who knows? But although originally conceived as maternity studies, the six British cohort studies launched between 1946 and 2000 contributed to much more than medical knowledge.
In the 1960s, they revealed that the brightest children do just as well in comprehensives as in grammar schools. And it was the 1958 cohort study that revealed, by administering its own intelligence tests on its subjects, that bright, working-class children were less than half as likely to win places in grammar schools as equally intelligent, middle-class children – a finding that Labour used to drive its massive expansion of comprehensives in 1965.
In the early 70s, the studies showed that divorce itself has less of a negative impact on children’s life choices than the resultant poverty into which it often throws single mothers. (A finding duly ignored by the government, but that’s another story…)
And it may seem obvious now that smoking causes lung cancer, but in 1951 when 80 per cent of men smoked and only a fraction of those got lung cancer, the causal link was far from given. By launching a cohort study on 41,000 British doctors, and working out exactly what evidence was required to prove that smoking caused cancer (rather than, for example, lung cancer having some bizarre side-effect of making people want to smoke), researchers were able to alert the public to a massive public health risk.
So what about the people behind the cohort studies?
When the 70th anniversary of the first British cohort study was celebrated in March this year, the BBC made a big song-and-dance about the group’s surviving members. And as the septuagenarians’ anniversary party appeared on just about every radio and TV news broadcast that day, I admit feeling a little burned out on cohort-study excitement long before I picked up this book.
But the volume is a gem for its depiction of the characters – and entities – behind the scenes: the doctor who doggedly pursued his interest in the lives of the thousands of individuals under his watch, fighting to keep the studies alive; the bicycle that transported millions of punch cards across London to be counted on a tabulating machine (described as the 1950s equivalent of a high-speed data link); the 9,000 placentas that are still in a storage shed near Bristol.
Also fascinating is the relationship between the data scientists, politicians and the media, as findings get headlined, distorted or buried – as suits the political or news agenda – to the continual frustration of the academics dedicating their lives to extracting meaningful findings from the tens of millions of data points.
Now every time I read “cohort study” on a piece of research, I admit I get a little bit excited…