Biostats Flashcards
testing frequency of disease and frequency of risk related factors
asks “what is happening?”
cross-sectional study
compares a group of people with disease to a group without disease
looks to see if odd of prior exposure or risk factor differ by disease state
asks “what happened?”
case control study
compares a group with a given exposure or risk factor to a group without such exposure
looks to see if exposure or risk factor is associated with later development of disease
cohort study
are cohort studies prospective or retrospective
can be either
compares frequency with which both monozygotic twins vs both dizygotic twins develop the same dz
twin concordance study
compares siblings raised by biological vs adoptive parents
adoption study
what does the likelihood ratio mean
likelihood that a given test result would be expected in a patient with the target disorder
compared to
the likelihood that the same result would be expected in a patient without the target disorder
LR+ > 10 indicates highly specific test
LR- < 0.1 indicates highly sensitive test
hawthorne bias
subjects changing behavior when they know they’re being observed
berkson bias
cases and/or controls selected from hospitals are less healthy and have different exposures than general population
attrition bias
participants lost to follow up have a different prognosis than those who complete the study
recall bias
patients with disease recall exposure after learning of similar cases
measurement bias
information is gathered in a systemically distorted manner
ex: using a faulty automatic sphygmomanometer to measure BP
procedure bias
subjects in different groups are not treated the same
ex: patients in treatment group spend more time in highly specialized hospital units
observer-expectancy bias
researcher’s belief in the efficacy of a treatment changes the outcome of that treatment (pygmalion effect)
ex: an observer expecting treatment group to show signs of recovery is more likely to document positive outcomes
confounding bias
factor related to both exposure and outcome (but not on causal path) distort effect of exposure on outcome
ex: an uncontrolled study shows an association between drinking coffee and lung cancer, however coffee drinkers also smoke more, which can account for the association
lead time bias
early detection is confused with increased survival
lag time bias
screening test detects disease with longer latency period, while those with shorter latency period become symptomatic earlier
ex: a slowly progressive cancer is more likely detected by a screening test than a rapidly progressive cancer
compare relative risk, relative risk reduction, attributable risk, and absolute risk reduction
relative risk: risk of developing disease
relative risk reduction: the proportion of risk reduction attributable to the intervention as compared to the control
attributable risk: difference in risk between exposed and unexposed groups
absolute risk reduction: difference in risk attributable to intervention as compared to the control
phase 1 trial of clinical trial
small number of healthy volunteers or patients with disease of interest
phase 2 of clinical trial
moderate number of patients with disease of interest
phase 3 of clinical trial
large number of patients randomly assigned to either treatment under investigation or the standard of care (placebo)
phase 4 of clinical trial
postmarketing surveillance of patients after treatment is approved
with receiving operating characteristic curves (ROC curves), what indicates a test with higher accuracy
higher area under the curve
(a test with 0 accuracy is a straight diagonal line, higher accuracy causes the line to curve upwards)
the highest accuracy causes the curve to form a rectangle shape
how to calculate standard error
SE = standard deviation / square root of sample size (n)
how to calculate confidence interval
CI of mean = mean +/- (z score for confidence level) x SE
Z score:
- 68%: CI - 1
- 95% CI - 1.96
- 99%: CI - 2.58
how does sample size affect power
increased sample size –> increased power
