BS - Epi/Biostat (Bias & study errors) Flashcards
(16 cards)
What is the type of bias related to recruiting participants?
Selection bias
What defines selection bias? What is its most common form?
Nonrandom assignment to participate in a study group. Most commonly a sample bias.
What are 3 types of selection bias? Give an example of each.
(1) Berkson bias: A study looking only at inpatients (2) Loss to follow-up: Studying a disease with early mortality (3) Healthy worker & volunteer biases: Study populations are healthier than the general population
What are 2 strategies for reducing selection bias?
(1) Randomization (2) Ensure the choice of right comparison/reference group
What are 4 types of bias related to performing a study?
(1) Recall bias (2) Measurement bias (3) Procedure bias (4) Observer-expectancy bias
What defines recall bias? What is an example of this? In what kind of studies is it common?
Awareness of disorder alters recall by subjects; Patients with disease recall exposure after learning of similar cases; Common in retrospective studies
What is the strategy to reduce recall bias?
Decrease time from exposure to follow-up
What defines measurement bias? What is an example of this?
Information is gathered in a way that distorts it; Hawthorne effect - groups who know they’re being studies behave differently than they would otherwise
What is the strategy to reduce measurement bias? For what other 2 types of bias does the strategy also work?
Use of placebo control groups with blinding to reduce influence of participants and researchers on experimental procedures and interpretation of outcomes; (1) Procedure bias (2) Observer-expectancy bias
What defines procedure bias? What is an example of this?
Subjects in different groups are not treated the same; Patients in treatment group spend more time in highly specialized hospital units
What defines observer-expectancy bias? What else is this called? What is an example of this?
Researcher’s belief in the efficacy of a treatment changes the outcome of treatment (aka Pygamlion effect; self-fulfilling prophecy); If observer expects treatment group to show signs of recovery, then he is more likely to document positive outcomes
What are 2 types of bias related to interpreting results?
(1) Confounding bias (2) Lead-time bias
What defines confounding bias? What is an example of this?
When a factor is related to both the exposure and outcome, but not in the causal pathway => factor distorts or confuses effect of exposure on outcome; 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
What are 3 strategies used to reduce confounding bias?
(1) Multiple/Repeated studies (2) Crossover studies (subjects act as their own controls) (3) Matching (patients with similar characteristics in both treatment and control groups)
What defines lead-time bias? In what context is it seen? What is an example of lead-time bias?
Early detection is confused with increased survival; seen with improved screening techniques; Early detection makes it seem as though survival has increased, but the natural history of the disease has not changed
What is the strategy for reducing lead-time bias?
Measure “back-end” survival (adjust survival according to the severity of the disease at the time of diagnosis)
