A weakness of circadian rhythm?

-Generlisation -Studies of the sleep wak cycle use samll groups or even 1 person like Siffre. Siffre observed that in his second study his internal clock was much slower -Ppts might not be representative fo the wider population and this limits making meaningful generalisations. -This meant that it is difficult to use the research data as it dissucces evertyhing as more than avarage which is meaningless