While it's shoddy statistics, at least in this case the implied effect seems to be real.
According to these two sources [1][2] that just came up when I searched for this, prevalence of wearing life-jackets among kayakers appears to be ~78%.
Note though that getting base rates from one place and getting rates of accidents from another is usually a bad idea: they will have various ways of measuring the rates, so will have different biases (based on location, time-of-day, time-of-year, ... where the measurement happens).
Note though that getting base rates from one place and getting rates of accidents from another is usually a bad idea: they will have various ways of measuring the rates, so will have different biases (based on location, time-of-day, time-of-year, ... where the measurement happens).