bag, and then given the choice of two bags: one containing 1 red ball and 9 white balls, the other having 8 red balls and 92 white balls. The majority chose the bag with 8 red balls, presumably reflecting a view that it gave more opportunities to win, even though the underlying chance was lower. Similarly people confronted with the statement " Cancer kills 2,414 people out of 10,000 " rated cancer as more risky than those told " Cancer kills 24.14 people out of 100 ". The potential influence of the size of the numerator and denominator is known as the 'ratio bias'. Frequencies are generally used in risk communication, but it is important to keep a common denominator in all comparisons: for example to describe what is expected to happen to 1000 women who go for screening for breast cancer, no matter whether they benefit or are harmed by the test. Comparing Percentage and Natural Frequencies Positive / negative framing What would you prefer, a game in which you had a 10% chance of winning, or one with a 90% chance of losing? You may shake your head and say that they are exactly the same, but it has been shown that it can make a big difference whether an outcome is expressed positively or negatively. For example, in a classic experiment, one group of people were told 'Of 100 people having surgery for lung cancer, 10 will die during treatment, 32 will have died by one year