Recall bias

Information bias (observation bias) Occurs when there are quality (accuracy) problems in the collection, recording, coding, or analysis of data among comparison groups. Interviewers might, e.g., interview the cases with more diligence than they interview the control, or a person with a disease may recall previous exposures better than persons who are healthy (this type of bias is called recall bias). 

A two- to threefold increased risk of birth defects among children of Vietnam war veterans exposed to Agent Orange has been suggested by several epidemiological studies, but these studies have been criticized on a number of grounds, including exposure assessment, outcome verification, and potential for recall bias. Animal studies have not demonstrated clear-cut adverse effects of phenoxyherbicide exposure on reproductive outcomes. ... 

Information bias can result from misclassiftcation of characteristics of individuals or events identified for study. Recall bias, one type of information bias, may occur when respondents with specific exposures or outcomes recall information differently from those without the exposures or outcomes. Interview bias may result when the interviewer knows a priori the category of exposure (for cohort studies) or outcome (for case-referent studies) in which the respondent... 

These investigations have shown significant associations with several types of cancer, but the most consistent findings have been for soft-tissue sarcoma and non-Hodgkin lymphoma. Although the odds ratios in some case-control studies may have been inflated by recall bias, this cannot explain all of the findings. Nor are they likely to have arisen by chance. It is not possible, however, to exclude a confounding effect of polychlorinated dibenzo-para-dioxins which occur as contaminants in chlorophenols. 

Furthermore, because many of the outcome measures used in these studies are based on self-report, they are also vulnerable to the frequently found discrepancy between self-assessment of sleepiness/alertness level and actual physiological level of sleepiness on the one hand (10,13) and recall bias on the other thus results... 

Both interview and register data have their pitfalls. Inaccuracy of spontaneous abortion recall has been observed in retrospective questionnaire studies (2, 3). Response bias and some evidence of recall bias has also been reported (2, 4). The use of registered data may help to avoid these problems. 

TCDD and exact levels of exposure were not known. Furthermore, in some studies the exposure data were based solely on questionnaires and some recall bias could have been present. Other studies suffered from examining small cohorts or investigating the effects after a short latency period. The long latency period is important for detecting increases in soft-tissue sarcomas, presumably a major cancer outcome of CDD exposure in humans. 

Study bias may be selection bias or information bias. Selection bias may occur in the choice of subjects for the study (e.g. exclusion of individuals who are not fluent in a particular language). Selection bias may also result from an individual s reluctance to participate in a study owing to concerns over a perceived exposure, resultant health effect, or educational and socioeconomic status of the participants. Parents who perceive that an exposure in their child s environment may have resulted in an adverse health effect may feel responsible for not protecting their child. Information bias may result from inappropriate classification of the individual study participants or from the information provided. For example, interview bias may result when an interviewer is not blind to the exposure of the test population. Recall bias may result when participants with specific exposures or effects respond differently from those without the specific exposures or effects. 

The major advantage of cohort studies is that exposure is measured before disease occurs and thus provides strong evidence of causality, given that the exposure of interest will be unlikely to be affected by disease status. Other advantages of cohort studies are that they allow measurement of disease in the exposed and unexposed population, can measure multiple outcomes, can evaluate rare exposures, and are not subjected to some types of biases, such as recall bias (see Section 26.2.4 for a description of biases). Disadvantages include (a) the requirement of large number of subjects, (b) expense, (c) requirement of an extensive time to set up and follow up, (d) cannot be used to evaluate rare diseases, and (e) can be associated with some type of biases such as selection bias. 

Differential misclassification occurs when the classification of disease is dependent on the exposure status or the classification of exposure is dependent on the disease status. Differential misclassification can bias the RR in either direction, and often the direction is unknown. Some examples of differential misclassification of exposure are recall bias and observer bias. Recall bias, which is limited to case-control studies, occurs when the cases remember exposure differently than healthy controls this type of bias usually results in finding a greater effect than what is real. Observer bias can occur if the observers, such as study interviewers, incorrectly assign exposure because they know the outcome status of an individual, or it can occur in the follow-up of disease if the observer knows the exposure status of the subject. Ideally, the observer should be blind to the outcome or exposure status of the study subjects. 

The accuracy of exposure assessment is determined by systematic and random errors in the assessment. For quantitative exposure assessments, important sources of error include measurement errors (i.e. from laboratory and field monitoring techniques), as well as variations in exposure over time and space. For qualitative exposure proxies (e.g. self-reported past exposures, occupational histories or expert evaluations), the most important sources of error are recall bias (systematic differences in exposure recall between cases and controls) and random error, expressed in terms of intra- and inter-rater agreement. Although systematic errors can result in serious misinterpretations of the data, especially due to scaling problems, random errors have received more attention in epidemiology because this type of error is pervasive, and its effect is usually to diminish estimates of association between exposure and disease. The magnitude of random errors can be considerable in epidemiological field studies. 

Cross-sectional studies can identify prevalence rates based on the distribution of a particular syndrome or malformation, but the study design makes it difficult to identify cause and effect relationships. Case-control protocols match the affected pregnancy to an unaffected pregnancy but, again, it is difficult to account for maternal recall bias and perhaps equally difficult to control for bias (even unconscious) on the part of the investigator. Cohort smdies, while suffering from problems of dose determination, are usually prospective, the largest, the most expensive, the slowest, and usually the most statistically powerful to detect reliable associations. Double-blind intervention studies, like those conducted with folic acid and prevention of NTD, usually yield the most conclusive data. 

Case-control studies identify an outcome (congenital anomaly), match subjects with and without that outcome, and report how often there was exposure to a suspected agent. The concern with this type of study is recall bias, because a woman with an affected pregnancy may be more likely to recall drugs used during the course of pregnancy than would a woman who had a normal pregnancy outcome. ... 

Recall bias occurs some time after an exposure and distorts the measurement of stress. The victim retrospectively reports more symptoms than would be recalled within 24-48 hours of the exposure (Hopwood and Guidotti 1988). The media can induce biased reporting by victims, and investigators using symptom checklists may suggest symptoms to victims. Bias also may result from victims skepticism about the veracity of manufacturers reports of the known toxic properties of commercial chemicals (Lees-Haley and Brown 1992). 

Holden C Love Canal residents under stress. Science 208 1242-1244,1980 Hopwood DC, Guidotti TL Recall bias in exposed subjects following a toxic exposure incident. Arch Environ Health 43 234-237,1988 Houts PS, McDougall V Effects of informing workers of their health risks from exposure to toxic materials. Am J Ind Med 13 271-279, 1988 Johnson DM The phantom anesthetist of Mattoon a fieid study of mass hysteria. J Ahnorm Soc Psychol 40 175-186,1945... 

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