A comparison of responses to a health and lifestyle questionnaire completed before and then after blood pressure screening DANIEL BARRY a AND MICHAEL J. HOGAN b a Department of Mathematics and Statistics, University of Limerick, Limerick, Ireland b Department of Psychology, NUI-Galway, Galway, Ireland Changes over a 2 - week period in self - reported health and lifestyle information were examined and related to medical feedback provided prior to the second self - report. The study group consisted of 128 females and 73 males ranging in age from 35 to 85 with a mean age of 55.5 years. On two occasions subjects completed self - assessment questionnaires including 52 items covering symptomatology and various lifestyle behaviours. Before the second self - assessment, subjects were classified as cases if their blood pressure was borderline or hypertensive according to World Health Organization guidelines or as controls otherwise. Subjects were informed of this classification. Across questions, the percentage disagreement between reports ranged from 0.0% to 44.1% with a median of 17.5% and with case – control differences significant at the 10% level for four questions. The mean difference between responses was significantly different from 0 at the 10% level for 15 questions with case – control differences significant at the 10% level for 6 questions. For 2 questions, the significance level of the association of response with case – control status changed from a value greater than 20% based on responses before feedback to a value less than 5% based on responses after feedback. Some evidence of recall bias was found. Journal of Exposure Analysis and Environmental Epidemiology ( 2002 ) 12, 244 – 251 doi:10.1038/sj.jea.7500223 Keywords: questionnaire, recall bias, recall error. Introduction Case – control studies, in which information concerning some past exposure is compared in those with and those without some particular disease, are particularly useful for investigating potential risk factors for diseases that are relatively rare. The methods used to ascertain exposure status are critical to the validity of a case–control study. When these methods rely on self - reports of past exposure, there is the potential for erroneous recall to occur with a consequent bias in the estimation of the association between exposure and disease status. In a situation where errors occur randomly and in a similar fashion for both cases and controls, the effect of such errors is to reduce the power of the study and to make it more difficult to establish an association between exposure and disease. However, in a situation where the pattern of errors is different for cases than it is for controls, there is considerable potential for the errors to produce misleading conclusions regarding the association between exposure and disease. Lippman and Mackenzie (1985) refer to this phenomenon as recall bias. Many attempts have been made to quantify the accuracy of self - reported exposure assessments. One type of study involves a comparison between self-reported exposure and exposure as determined by a suitable biochemical marker. Cotinine has been widely used as a marker for exposure to nicotine in the context of both active (Patrick et al., 1994) and passive smoking ( Barry, 1997 ). A second type of study involves a comparison between self-reported exposure and exposure as determined from medical records. Examples of such studies occur in the context of elective abortion ( Lindefors - Harris et al., 1991 ), in the context of drug usage (Paganini-Hill and Ross, 1982), and in the context of oral contraceptive use ( Stolley et al., 1978 ). A third type of study involves a comparison between self-reported exposure and exposure as reported by a surrogate respondent, usually the next of kin. Examples of such studies occur in the context of environmental tobacco smoke (ETS) exposure (Nyberg et al., 1998 ), in the context of dietary information (Humble et al., 1984 ), and in the context of medical, smoking, and dietary consumption data ( Herrmann, 1985 ). A fourth type of study is the so-called test–retest study involving a comparison between self - reported exposure assessments taken at two separate time points. The best design for such a study involves one exposure assessment before determination of case –control status and a second assessment after determination. Such studies are usually undertaken as part of a case–control study nested within a 1. Address all correspondence to: Dr. Daniel Barry, Department of Mathematics and Statistics, University of Limerick, Limerick, Ireland. Tel.: + 353 - 61 - 202328. Fax: + 353 - 61 - 334927. E - mail: don.barry@ul.ie Received 8 April 2002. Journal of Exposure Analysis and Environmental Epidemiology (2002) 12, 244 – 251 # 2002 Nature Publishing Group All rights reserved 1053-4245/02/$25.00 www.nature.com/jea