A district officer reports that accidents involving cyclists made up 12 per cent of all road accidents in the district five years ago and only 8 per cent last year, and concludes from this that cycling in the district has become safer. Which of the following, if true, most seriously undermines that conclusion?

A share can shrink simply because the rest of the total grew faster. If accidents overall more than doubled, then 8 per cent of the new total exceeds 12 per cent of the old one, and more cyclists are being hurt than before - the opposite of the officer's claim. Helmet use and new cycle tracks bear on safety but not on the reading of the percentage, and the reporting habit was in place across both years.