Medical researcher: Scientists compared a large group of joggers who habitually stretch before jogging to an equal nu...

SamA on November 11, 2019

Hello @Meredith,

Answer choice D tells us that the habitual stretchers were probably more injury prone than the average jogger. If this is true, then it is possible that the stretching habit reduced their injury rate to the point that it is equal to the non-stretching joggers. This shows that the flat-out comparison between stretchers and non-stretchers, without factoring in their injury proneness, is not strong enough evidence to support the conclusion. The stretching group could have reduced their injury rate, which would contradict the conclusion.