A statistical term describing a systematic in?uence which leads to consistent over- or underestimation of the true value. For example, if a researcher is studying the effects of two di?erent drugs on the same disease and personally favours one, unless they have been blinded to which patient is receiving which treatment, they may unwittingly cause bias in the results by regarding those treated with their preferred drug as being healthier.
In general, any factor that distorts the true nature of an event or observation. In clinical observations, a bias is any systematic factor other than the intervention of interest that affects the magnitude of an observed difference (i.e. trends to increase or decrease) in the outcomes of a treatment group and control group. Bias diminishes the accuracy (though not necessarily the precision) of an observation. Randomization is a technique used to decrease this form of bias. Bias also refers to a prejudiced or partial viewpoint that would affect someone’s interpretation of a problem. Double-blinding is a technique used to decrease this type of bias. See “blinding”.
n. systematic deviation of results from the truth. The many different types of bias include selection bias (failing to select a sample that is representative of the wider population), nonresponse bias (respondents differing from nonrespondents in statistical surveys), social desirability bias (respondents giving false answers they believe to be more socially acceptable than the truth), and systematic measurement errors (all measurements deviate from the truth in the same systematic fashion).
Occurs when some participants who are assigned to the treatment group in a clinical study do not receive the intervention or receive another intervention, or when some participants in the control group receive the intervention (e.g. outside the trial). If these crossover participants are analysed with their original groups, this type of bias can “dilute” (diminish) the observed treatment effect.... crossover bias
Unrepresentative publication of research reports that is not due to the quality of the research but to other characteristics, e.g. tendencies of investigators to submit, and publishers to accept, positive research reports (i.e. ones with results showing a beneficial treatment effect of a new intervention).... publication bias
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