What would worry you more: being told that cancer kills 25 people out of 100, or that it kills 250 people out of 1000? Dumb question, you might say; both statements mean that a quarter of people die of cancer.
Yet such differences do matter 鈥� not to the risk itself, but to our perception of it. Those wishing to play up or play down a risk, whether to sell newspapers or a medical treatment, can follow the simple rule of 鈥渞atio bias鈥�. The bigger the number, the riskier the risk appears.
In one study of this effect, people rated cancer as riskier when told that it 鈥渒ills 1286 people out of 10,000鈥� than when told it 鈥渒ills 24.14 people out of 100鈥�, even though the second statement equates to almost double the risk (). Similarly, 100 people dying from a particular form of cancer every day can be perceived as a lesser risk than 36,500 dying from the same disease each year, although the two are equivalent statements ().
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So when confronted with questions of risk, look carefully at the way the numbers are presented. And if you are comparing risks, make sure they are divided by the same number.
Read more: 鈥�Spin doctors: The truth behind health scare headlines鈥�
