USMLE Step 1 Biostatistics/Epidemiology Questions And Answers Graded A+
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Module
USMLE Step 1 Biostatistics/Epidemiology
Institution
USMLE Step 1 Biostatistics/Epidemiology
Adoption study - compares siblings raised by biological vs adoptive parents
measures heritability and influence of environment
Observer-expectancy effect - Occurs when a researcher's belief in the efficacy of a treatment
changes the outcome of that treatment
Chi square - tests the difference be...
USMLE Step 1
Biostatistics/Epidemiology
Adoption study - compares siblings raised by biological vs adoptive parents
measures heritability and influence of environment
Observer-expectancy effect - Occurs when a researcher's belief in the efficacy of a treatment
changes the outcome of that treatment
Chi square - tests the difference between 2 or more percentages or proportions of categorical
outcomes (NOT THE MEAN VALUES)
ANOVA - checks difference between the means of 3 or more groups
Attributable Risk - (a / (a+b) ) - (c / (c+d) )
Case control study - compares a group of people with a disease to a group of people without a
disease
Asks, what happened?
Measures odds ratio
Cohort study - Compares a group wit ha given exposure or risk factor to a group without the
exposure
Asks who developed disease?
Measures relative risk
, Confidence Interval - range from [mean - Z (SEM)] to [mean + Z (SEM)]
Z = 1.96 for 95% CI
Z = 2.58 for 99% CI
On the test, it may be easier to remember the Z values as 2 and 2.5 for easier calculations and
memorization
Confounding Bias - Occurs when factor is related to both exposure and outcome, but is not the
the causal pathway; factor distorts or confuses effect of the exposure on outcome
Cross-sectional study - Collects data from a group of people to asses frequency of disease
Hawthorne effect - Occurs when the group being studied changes its behavior because they know
they are being studied
This looks at new incidences occurring during a time period
Late-Look Bias - Information gathered at an inappropriate time (like surveying dead people)
Lead-time Bias - Early detection confused with increased survival; seen with improved screening
(the natural history of the disease is not changed but catching things earlier, like cervical cancer, makes it
seem as though survival increased)
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