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.
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”.... bias
A trial in which each of the groups involved will receive each of the treatments, but in a randomized order: that is, they will start in one arm of the trial, but will deliberately ‘cross over’ to the other arm(s) in turn.... crossover trial
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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