Problems include differentiating between voluntary and involuntary risk, and between fatal and minor outcomes. For example people felt with the Schering Chart it would be better to compare alternative methods of contraceptive, since there was an element of choice, whereas there was not an alternative to crossing the road. People are much more likely to accept risks that are taken voluntarily. Drugs often carry a risk of side effects but these are acceptable for the sake of a cure. Even statisticians have attempted to quantify risk with a score that accounts for the number of likely deaths resulting from large scale catastrophes but this has yet to be tested on the public.
Risks are also subject to fashion.
The risk of death due to meningitis has not changed recently, but it is now customary for newspapers to report deaths of students over the winter. The fear of child molesters has instituted major social changes in the way children are brought to school and in their social activities, despite the lack of evidence that is any more dangerous for children out of doors now than fifty years ago. Other fashions have come and gone, without noticeable change in the underlying risk, such as listeria and necrotising fasciitis. Currently we are worrying about new variant CJD, which carries a risk, at present, of about 1 in 2,000,000. Because of the Bristol scandal, we are now worrying about risk of surgery, and patients will start demanding comparative risk figures for different surgeons in the same way as they require school performance figure.