Sense about Science ? equipping people to make sense of science and evidence
For the record
"A sausage a day could lead to cancer"
The Daily Mail, the Guardian, Mirror and Daily Express report a study suggesting that eating 100g of processed meat a day raises the risk of developing pancreatic cancer by 38% and eating 150g a day raises it by 57%. To understand the significance of any increase or decrease in risk for an individual we need to know what the risk was in the first place. In other words it is important to know not only the relative percentage risk but also the absolute risk.
Nigel Hawkes, Director of Straight Statistics looks at the change in absolute risk: “According to the researchers the risk of developing pancreatic cancer is one in 77 for men and one in 79 for women. Pancreatic cancer has a very poor prognosis, so the risk of getting it is more or less identical to the risk of dying from it. Office of National Statistics mortality figures show 7,146 people dying of pancreatic cancer in 2009, out of a total of 489,097 deaths, i.e. one in 68.
If eating one less sausage a day reduced the risks by 19 per cent, as the paper suggests, the risk would be reduced to one in 84. The deaths saved per year would be 1,357. If we take the population of the UK to be 60 million, and assume 50 million eat sausages (subtracting infants and vegetarians) then more than 36,000 people would have to make this dietary change to save one death per year.”
In our Making Sense of Statistics guide writer and broadcaster Michael Blastland said: “Why do reports prefer to talk about relative percentage risks without mentioning the absolute risk? The suspicion must be that this allows the use of ‘bigger numbers’: 20% is big enough to be a scare, an absolute change of 1% or even 1 person in every 100, is less disturbing.”
Document type: For The Record
Published: 13 January 2012