The Art of Statistics: Learning from Data

by David Spiegelhalter

Epidemiology is the study of how and why diseases occur in the population, and Scandinavian countries are an epidemiologist’s dream. This is because everyone in those countries has a personal identity number which is used when registering for health care, education, tax, and so on, and this allows researchers to link all these different aspects of people’s lives together in a way that would be impossible (and perhaps politically controversial) in other countries. A typically ambitious study was conducted on over 4 million Swedish men and women whose tax and health records were linked over eighteen years, which enabled the researchers to report that men with a higher socioeconomic position had a slightly increased rate of being diagnosed with a brain tumour. This was one of those worthy but rather unexciting studies that would typically not attract much attention, so a university communications officer thought it would be more interesting to say in a press release that ‘High levels of education are linked to heightened brain tumour risk’, even though the study was about socioeconomic position rather than education. And by the time this got to the general public, a subeditor in a newspaper produced the classic headline, ‘Why Going to University Increases Risk of Getting a Brain Tumour’.1 For anyone who has spent time accumulating academic qualifications, this newspaper headline could have been alarming. But should we be concerned? This is a huge study based on a registry of ...

Epidemiology and completion bias