Methodological issues in studies

• The findings from the Campbell and Murphy study have yet to be replicated
• other psychologist have been critical of the manner in which the study was conducted and have suggested that there may have been some limited light exposure to the participants’ eyes- a major confounding variable
• also isolating one exogenous zeitgeber in this way does not give insight into the many other zeitgebers that influence the sleep/wake cycle and the extent to which these may interact