Recall bias in self-reported melanoma risk factors

The evidence implicating sun exposure in the etiology of melanoma derives l argely from case-control studies in which the retrospective assessment of s un exposure suggests potential for significant recall bias. Previous attemp ts at characterizing and quantifying that bias have had significant methodo logical limitations. In the International Twin Study, a case-control study of melanoma risk factors in twins conducted from 1980 to 1991, the authors asked melanoma cases and their co-twins to quantify their own exposures and asked which twin had the greater exposure. Recall bias was investigated by assuming that, if bias had occurred, the odds ratio based on the case's re sponse would differ significantly from the odds ratio based on the co-twin' s response. Case-derived odds ratios were higher than the odds ratios for t he controls for sunbathing in childhood and adulthood and for mole frequenc y and freckling in childhood, suggesting some recall bias. The odds ratios for ease of burning and tanning appeared unbiased. The belief that sunlight was a cause of melanoma appeared related to an increased odds ratio for su nbathing as a child. There is a continuing need to carefully assess recall bias in the study of melanoma risk factors.