Bias And Study Errors Flashcards
Bias And Study Errors - recruiting participants
Selection bias
Bias And Study Errors - performing study
- Recall bias
- Measurement bias
- Procedure bias
- Observer-expectancy bias
Bias And Study Errors - Interpreting results
- Confounding bias
2. Lead time bias
Selection bias (type and definition)
Type: Recruiting participant bias
Error in assigning subjects to study group resulting in an unrepresentative sample. Most commonly a sampling bias
Selection bias examples
- Berkson bias (from hospitals)
- Healthy worker effects
- Non-response bias
Strategy to reduce selection bias
- Randomization
2. Ensure the choice of the right comparison/reference group
Berkson bias
Type of selection bias
Study population selected from hospital is less healthy than general population
Healthy worker effect
Type of Selection bias
Study population is healthier than general population
Non-response bias
Type of Selection bias
Participating subjects differ from nonrespondents in meaningful ways
Recall bias (type and definition)
Type: performing study
Awareness of disorder alters recall by subjects. Common in retrospective studies
Recall bias example
Patients with disease recall exposure after learning of similar cases
Recall bias strategy to reduce
Decrease time from exposure to follow up
Measurement bias (type and definition)
Type: performing bias
Information is gathered in a way at distorts it
Measurement bias example
Miscalibrated scale consistently overstates weights of subjects
Measurement bias strategy to reduce
Use objective, standardized and previously tested method of data collection that are planned ahead of time
Procedures bias (type and definition)
Performing study
Subjects in different group are not treated in the same way
Procedure bias example
Patients in treatment group spend more time in highly specialized hospitals units
Procedure bias strategy to reduce
Blinding and use of placebo reduce influence of participant and researchers on procedures and interpretation of outcomes as neither are aware of group allocation
Observer-expectancy bias (type and definition)
Type: Performing study
Researchers belief in the efficacy of the treatment changes the outcome of that treatment (aka Pygmalion effect, self-fulfilling prophesy)
Observer-expectancy bias example
If observer expects treatment groups to show signs of recovery, then he is more likely to document positive outcomes
Observer-expectancy bias strategy of reduction
Blinding and use of placebo reduce influence of participant and researchers on procedures and interpretation of outcomes as neither are aware of group allocation
Bias And Study Errors types
- Recruiting participants
- Performing study
- Interpreting results
Interpreting results bias types
- Comfounding bias
2. Lead times bias
Comfounding bias (types and definition)
Type: Interpreting bias
When factor is related to both exposure and outcomes, but not to the causal pathway –> factor distorts or confuses effects on outcome
Confounding bias example
Pulmonary disease is more common in coal workers than the general population. However, people who work in coal mines also smoke more frequently than the general population
Confounding bias strategy of reduction
- Multiple/repeated studies
- Crossover studies (subjects act as their own controls –> persons in group 1 receive the drug and group 2 placebo. Later they swich)
- Matching (patient with similar characteristics in both treatment and control groups)
- Restriction
- Randomization
Lead-times bias type and definition
Type: interpreting results
Early detection is confused with increased survival
Lead time bias example
Early detection makes it seems as though survival has increased, but the natural history of the disease has not changed
Lead time bias strategy of reduction
Measure “back end” survival (adjust survival to the severity of disease at the time of diagnosis)
Recall bias is common in
Retrospective bias
Observer expectancy bias is also called
- Pygmalion effect
2. Self-fulfilling prophecy
Pygmalion effect is aka
- Observer expectancy
2. Self-fulfilling prophecy
Crossover studies
subjects in group 1 receive the drug and group 2 placebo. Later they switch –> subjects act as their own control
types of bias - groups
- recruiting participants
- performing study
- interpreting results
