Whilst I’d agree excessive use of CP is, almost certainly, a sign of abuse, a simple higher-than-average rate could indicate the exact opposite.
Consider two schools ‘A’ and ‘B’. In ‘A’, over a given period of time, x% of pupils are caned. In ‘B’, over the same period of time, 1.9x% of pupils are caned. At first sight, we might think school ‘B’ is using the cane excessively. The (mean) average is 1.45% so school ‘A’ appears to be using it reasonably sparingly. However, if we find that ‘A’ has a policy of not using CP with girls (so uses it not according to the offense, but according to the sex of the offender) whilst ‘B’ uses it equally, regardless of the sex of the offender, the picture reverses. In ‘B’ 1.9x% of pupils were caned but in ‘A’ (presuming equal numbers of each sex) 2% of pupils liable to be caned were. ‘A’ is now above average and ‘B’ is below.