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Recall Bias: a Proposal for Assessment and Control

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Recall Bias: a Proposal for Assessment and Control International Journal of Epidemiology Vol. 16, No. 2 ©International Epidemiological Association 1987 Printed in Great Britain Recall Bias: A Proposal for Assessment and Control KAREN RAPHAEL Probably every major text on epidemiology offers at Whether the source of the bias is underreporting of least some discussion of recall bias in retrospective true exposures in controls or overreporting of true research. A potential for recall bias exists whenever exposures in cases, the net effect of the bias is to historical self-report information is elicited from exaggerate the magnitude of the difference between respondents. Thus-, the potential for its occurrence is cases and controls in reported rates of exposure to risk greatest in case-control studies or cross-sectional factors under investigation. Consequently, recall bias studies which include retrospective components. leads to an inflation of the odds ratio. It leads to the Downloaded from Recall bias is said to occur when accuracy of recall likelihood thai-significant research findings based upon regarding prior exposures is different for cases versus retrospective data can be interpreted in terms of a controls. methodological artefact rather than substantive The current paper will describe the process and con- theory. sequences of recall bias. Most critically, it will suggest methods for assessment and adjustment of its effects. It is important to note that recall bias is not equiva- http://ije.oxfordjournals.org/ lent to memory failure itself. If memory failure regard- ing prior events is equal in case and control groups, WHAT IS RECALL BIAS? recall bias will not occur. Rather, memory failure itself Generally, recall bias has been described in terms of will lead to measurement error which, in turn, will 'embroidery' of personal history by those respondents usually lead to a loss of statistical power. Loss of power who are cases. For example, Mausner and Kramer1 will bias hypothesis tests toward the null. In contrast, comment that 'people may be more likely to search for inequality of memory failure in cases versus controls leads to recall bias which, in turn, will bias hypothesis explanations for the disease in the cases and, there- by guest on July 15, 2016 fore, may assign more significance to past events' tests away from the null. (p. 165). A classic example is reported by Brown and The confusion between simple memory failure and Harris2 who comment on a 1958 study by Stott.3 Stott, differential memory failure is common in the litera- finding that mothers of 'mongol' children reported ture. For example, a 1967 study by Klemetti and more shocks during pregnancy than mothers of normal Saxen4 is often cited as evidence that recall bias exists children, concluded that socioemotional factors had an in retrospective studies of maternity outcome. How- aetiological role in mongolism. Later research, of ever, as noted by Lippman and Mackenzie,5 Klemetti course, indicated that chromosomal abnormalities and Saxen found that, while mothers' retrospective were the cause, and that ordinary events were prob- reports of drug use during pregnancy poorly corre- ably redefined as traumas by mothers of cases in an sponded with their prospective reports, the degree of effort to explain what happened. memory loss was not moderated by the outcome of the Perhaps less recognized as part of the recall bias pregnancy or condition of the child. Thus, there was no process is that those without the disease under support for anamnestic inequality between cases and investigation (ie controls) may be less likely to recall a controls. A similar confusion between simple recall true exposure. For example, mothers who have given difficulty and recall bias occurred in a recent report.6 birth to healthy infants may have less motivation to When comparing data on accuracy of two methods for recall earlier drug use during pregnancy than those collection of data on perimenstrual stress, the authors mothers whose infants had birth defects. note the unreliability of retrospective reports and state that their results are consistent with recall bias hypoth- Psychiatric Epidemiology Training Program. Columbia University. eses. However, they did not note differential unre- School of Public Health. Tower 3-20E, 100 Haven Avenue. New York. liability among cases and controls and, therefore, did NY 10032. USA. not support recall bias hypotheses. 167 168 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY Despite the attention given to recall bias in most METHODS OF ASSESSING AND ADJUSTING epidemiological texts, the research literature focusing FOR RECALL BIAS specifically on recall bias is extremely limited. A com- Given the possibility that recall bias may be operating, puterized literature search on the topic scanned four it becomes imperative to try to assess its effect in any data bases (ie Psychological Abstracts post-1967, Bio- case-control or cross-sectional study. logical Abstracts post-1977, Index Medicus post-1966 Recall bias can be ruled out when actual exposure and Science Citation Index post-1977) and found only status can be verified through unbiased records. Since 23 articles mentioning recall bias in their title or no unbiased records are available in most studies, this abstract. Five of these 23 articles were general approach has only limited application. In fact, if methodological papers on the case-control study. unbiased records are available, it would often seem Seven were critical reviews of epidemiological less expensive and more accurate to avoid the ques- research for a specific disease. Seven were studies in tioning of respondents at all regarding the verifiable experimental psychology of memory and cognition, exposures. and only some of these had application to recall bias in Recall bias is less likely to be invoked as a plausible epidemiological research. Finally, only four were explanation for research findings when other specific original research papers. Three of these four exposures have equal 'intuitive plausibility' as risk papers were in the field of maternity outcome. An factors for the disease under investigation, in com- additional manual search of the research literature parison to the significant exposure, yet the other Downloaded from suggests that case-control reports of maternity out- exposures are not significantly related to disease comes are more likely than other areas of research to status. For example, in a case-control study on mater- discuss recall bias. Recall bias appears to have been nal use of Bendectin and infant malformation,8 a sig- given somewhat less attention in other areas of epi- nificant odds ratio was found for Bendectin use. No demiological research. significant effects were found for other drugs used http://ije.oxfordjournals.org/ No claim can be made that a computerized literature during pregnancy. The authors convincingly argue search represents an all-inclusive search of articles dis- against the possibility of recall bias, because biased cussing recall bias. While many more original articles recall of exposure to a potential teratogen should be probably mention issues of recall bias in their discus- equal across the different agents. sion sections, the fact that so few studies mention recall Another possible method for assessing whether bias in their abstract suggests that the issue is recall bias is operating at all is to directly ask respond- ultimately accorded limited prominence in the con- ents to identify the exposures which they believe are clusions reached from the studies. relevant risk factors for the disease. To reduce sensi- by guest on July 15, 2016 Nevertheless, the same texts which recognize the tization, the questioning should occur following the possibility of recall bias in case-control studies usually completion of the' rest of the interview. If those risk note that the case-control design is the most appropri- factors which appear to be significantly related to case ate methodology for study of rare or chronic diseases status are not believed by respondents to be risk factors with long incubation or latency periods. Case-control for the disease at all, one possesses fairly good evi- designs are also most appropriate for generating dence against the existence of recall bias. However, hypotheses in newer areas of research and when work- what strategy can one apply in a study where the inves- ing under tight budgetary restrictions. Thus, although tigated exposures are plausible risk factors to the problems posed by recall bias may be substantial, the respondent? necessity for case-control designs suggests that these The strategy I propose is adapted from the logic of problems will be with us for some time to come. the validity scales of the Minnesota Multiphasic Per- While firm evidence for the presence of recall bias is sonality Inventory (MMPI),9 the most popular person- inconclusive,5 multiple studies have demonstrated its ality inventory to date."1 The authors of the MMPI existence in some areas of psychiatric research.7 A included in their multi-scale instrument a validity scale conservative approach in all areas of research would to correct or adjust some of the other scales, based dictate that a study be viewed as 'guilty until proven upon a measure of each respondent's test-taking atti- innocent'. It is not the task of one's critics to prove that tude or response set. recall bias exists; rather, I contend that it is the Similarly, a validity scale can be constructed to researcher's task to either present a strong case against adjust or correct for differential recall patterns among the existence of this threat to the study's validity and/or respondents. Construction of the validity scale will try to statistically control for recall bias in one's involve the researcher's identification of a number of analysis. previously evaluated exposures which have been ruled RECALL BIAS 169 out as risk factors for the disease under study. Each another estimate of the extent to which respondent item on the validity scale should question the respond- reports are biased by recall.
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