Bias Flashcards
Error in assigning individuals to groups leading to differences which may influence outcome.
Selection bias
bias where the subjects are not representative of the population
sampling bias (type of selection bias)
cases and controls in a hospital case control study are systematically different from one another because the combination of exposure to risk and occurrence of disease increases the likelihood of being admitted to the hospital
admission bias (Berkson’s bias)
Difference in the accuracy of the recollections retrieved by study participants
recall bias
Recall bias particularly problem in what study
case control
Failure to publish results from valid studies, often as they showed a negative or uninteresting result.
publication bias
clinicians may be reluctant to order the gold standard test unless the new test is positive, as the gold standard test may be invasive
Work up bias/verification bias
Only in non-blinded trials. Observers may subconsciously measure or report data in a way that favours the expected study outcome.
Expectation bias (Pygmalion effect)
Gathering information at an inappropriate time e.g. studying a fatal disease many years later when some of the patients may have died already
Late look bias
Occurs when subjects in different groups receive different treatment
Procedure bias
Occurs when two tests for a disease are compared, the new test diagnoses the disease earlier, but there is no effect on the outcome of the disease
Lead-time bias
A form of bias that occurs when measurement of information differs among study groups
Information bias
Types include recall bias, reporting bias, diagnostic bias, and Hawthorne effect, errors in measurement
information bias
Distortion of exposure, disease relation by some other factor
confounding bias
