Information bias

Bias Occurs when there is a tendency to produce results that differ in a systematic manner from the true values. A study with small systematic bias is said to have high accuracy. Bias may lead to over- or underestimation of the strength of an association. The sources of bias in epidemiology are many and over 30 specific types of bias have been identified. The main biases are selection bias, information bias, and bias due to confounding. 

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). 

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... 

Olsson and Brandt (1980) carried out a hospital-based case-control study of Hodgkin s disease and chemical exposures in Lund, Sweden. Twenty-five consecutive male cases aged 20-65 years were included. Two neighbourhood-matched controls were selected for each case from the Swedish population register. Interviews with study subjects focused on their detailed job history, and in particular exposure to solvents. Interview data were supplemented with visits to employers in some cases. Four of the cases and none of the controls had been exposed to xylene. All exposed cases were also exposed to other solvents. [The Working Group noted the opportunity for information bias, since the interviewer was not blind to disease status or to the study objectives ]... 

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. 

Selection bias Information bias Indication or protopathic bias Ingredient bias Dose bias... 

Selection bias = random selection of controls failed orthechosen control population is biased, information bias = methods used to obtain information about analgesic consumption were doubtful, indication (protopathic) bias = failure to control for analgesic intake preceding the development of renal failure,... 

However, Pearce et al. [14(NC)] have written that the problem of information bias is of particular concern in asthma epidemiology issues because of the difficulties in defining and measuring asthma, allergic rhinoconjunctivitis and atopic eczema, and the difficulties in obtaining exposure information in the aetiologically relevant time period. However, provided that the information has been collected in a standardized manner, then misclassification will be non-differential, and any bias it produces will usually be towards the null value. 

An advantage of the case-control design for the study of drug-outcome relationships is its efficiency for the study of rare or delayed outcomes. Compared with other strategies, the case-control study is relatively inexpensive. One potential problem with case-control studies is their susceptibility to certain types of bias, including selection bias and information bias. Selection bias refers to systematic differences between those selected for study and those who are not, whereas information bias is systematic differences in the quality of information gathered for study and comparison groups. 

Information bias—A flaw in measuring exposure or outcome data that results in systematic differences in the quality of information gathered for study and comparison groups. See also Selection bias. 

Selection bias—Systematic differences in characteristics between those selected for study and those who are not. See also Information bias. 

Information bias Ascertainment of cases varied from dermatological examination to self-administered questionnaires... 

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