Part 1 (research methodology) research studies of circadian rhythms suffer from flaw when estimating ‘free-running’ cycle of human circadian rhythms. The evidence shows participants were isolated from variables that could affect their circadian rhythms, such as clocks, radios and daylight. means results could be somewhat inaccurate. However, they weren’t isolated from artificial light as it was believed this would not affect their circadian rhythms whereas daylight would.