BS - Epi/Biostat (Bias & study errors) Flashcards
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
