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The scope for biased recall of risk-factor exposure in case-control studies: evidence from a cohort study of Scottish
Chris Metcalfe1, John Macleod, George Davey Smith
1Department of Social Medicine, University of Bristol, Bristol, UK. chris.metcalfe@bristol.ac.uk
Aims:
Case-control studies are prone to recall bias, a participant's case-control status influencing their recall of exposure to risk factors. We aimed to demonstrate empirically the scope for this bias.
Methods:
Two thousand five hundred and fifty men without coronary heart disease at enrollment to a prospective cohort study underwent two health assessments, about 5 years apart. The association between the development of coronary heart disease in the intervening period and changes in reported stress and cigarette smoking were investigated.
Results:
Men admitted to hospital with coronary heart disease reported a greater increase in psychological stress (p=0.032) and greater cessation of smoking (22% vs. 10%; p=0.007) than men not admitted. Consequently, when exposure data are collected at the end rather than at the start of the follow-up period, coronary heart disease is observed to be more strongly associated with psychological stress, and more weakly associated with smoking.
Conclusions:
At the time when a case-control study is conducted, levels of exposure to risk factors will have been influenced by disease development. When participants are asked about their level of exposure for a previous time period, recall is likely to be influenced by present outcome and exposure status, especially when psychological states are being investigated.
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