"One report on which the IARC [International Agency for Research on Cancer] based its findings showed a 36 per cent greater risk of breast cancer for women who had worked night shifts for more than 30 years, compared with women who had never worked nights."Professor Neil Pearce of Massey University says that the 36 per cent increase, while not trivial, is "not huge". But it's not clear that reporter Martin Johnson picked up on that message when he put 36% in big red letters in a special side box. People in general don't understand statistics, and you can bet that there are a considerable number of people who have read that and immediately thought that this statistic means:
- 36 per cent of women who work nights will get breast cancer
- if you work a single night shift, you will be 36 per cent more likely to get breast cancer
- 36 per cent of women work night shifts
- 36 per cent of night shifts will give you breast cancer
- working night shifts will give 36 per cent of your breasts cancer
- reading about night shifts will give you 36 cancers
And let's remember - this 36 per cent figure comes from a single study. And the contrast in criteria used by the original study and the Herald article (via a Massey University study - *ahem*) is informative: in the original report, 'night workers' were women who had worked night shifts for more than 30 years; in the Massey study quoted by the Herald and then extrapolated to find how many 'night workers' there are, it was anyone who had worked a night shift in the last four weeks. But that didn't stop the Herald putting (imagine big, red letters here) "50,000 women and 120,000 men work night shifts [in New Zealand]".
36 percent of 50,000 is 18,000. Oh. My. God...