Bias and study errors Flashcards
Interpreting results biases
- Confounding bias
2. Lead time bias
Define Lead time bias
Early detection makes think increase survival, but natural history same
Define confounding bias
Factor related to exposure and outcome, but not on causal pathway
Distort effect of exposure on outcome
Performing study biases
- Recall bias
- Measurement bias
- Procedure bias
- Observer expectancy bias
Define recall bias
Awareness of disorder alters recall by subjects
Common in retrospective studies
Define measurement bias
Info gathered in systematic disordered matter
Define procedure bias
Subjects in different groups are not treated the same
Define observer expectancy bias
Belief in treatment chase outcome
Self fulfilling prophecy
Recruiting bias
Selection bias
Define selection bias
Error in assigning subjects to study groups
Common in sampling bias
How reduce selection bias
Randomization
How reduce recall bias
Decrease f/u after exposure
How reduce procedure and observer expectancy bias
Blinding and use of placebo
How decrease confounding bias
Repeated studies Crossover studies Matching pts with similar characteristics into groups Restriction Randomization
How decrease lead time bias
Measure back end survival (adjust survival according to severity at time diagnosis)
