Biostatistics Flashcards
(24 cards)
cross-sectional study
measures disease prevalence and association (not causation) with different risk factors; collects data at a particular point in time
case-control study
measures odds ratio; retrospectively compares a group with a disease to a group without that disease to look for prior exposures or risk factors
cohort study
measures relative risk; prospectively or retrospectively compares a group with a particular exposure/risk factor to a group without that exposure/risk factor to look for increased likelihood of disease
twin concordance study
measures heritability and influence of environmental factors by comparing frequency with which both monozygotic twins vs. both dizygotic twins develop the same disease
adoption study
measures heritability and influence of environmental factors by comparing siblings raised by biological vs. adoptive parents
sensitivity
probability of a positive test when the disease is present; high-sensitivity tests used for screening in diseases with low prevalence
sensitivity = TP/(TP+FN) = 1 - false-negative rate
specificity
probability of a negative test when the disease is absent; high specificity test used for confirmation after a positive screening test
specificity = TN/(TN + FP) = 1 - false-positive rate
positive predictive value
proportion of positive test results that are true positives
PPV = TP/(TP + FP)
negative predictive value
proportion of negative test results that are true negatives
NPV = TN/(TN + FN)
odds ratio
odds that the group with the disease was exposed to a risk factor divided by the odds that the group without the disease was exposed
relative risk
risk of developing disease in the exposed group divided by risk in the unexposed group
attributable risk
the difference in risk between exposed and unexposed groups; the proportion of disease occurrences that are attributable to the exposure
relative risk reduction
the proportion of risk reduction attributable to the intervention compared to a control
RRR = 1 - RR
absolute risk reduction
the difference in risk attributable to the intervention as compared to a control
number needed to treat
number of patients who need to be treated for one patient to benefit
NNT = 1/ARR
number needed to harm
number of patients who need to be exposed to a risk factor for one patient to be harmed
NNH = 1/AR
standard error of the mean
an estimate of how much variability exists between the sample mean and the true population mean
SEM = SD/square root of sample size
type I error
false-positive error; stating that there is an effect or difference when none exists; probability is measured by alpha
type II error
false-negative error; stating that there is not an effect or difference when one exists; probability is measured by beta
power
the probability of rejecting the null hypothesis when it is false, i.e. finding a correct, positive result; power = 1 - beta
confidence interval
range of values in which a specified proportion of the means of repeated samples would be expected to fall
CI = mean +/- Z(SEM)
For 95% CI: Z = 1.96
For 99% CI: Z = 2.58
t-test
check differences between the means of two groups
ANOVA
check differences between means of three or more groups
chi-square
check differences between two or more percentages or proportions of categorical outcomes
