epi/biostats

Question 1

cross-sectional study

Answer 1

collects data from group to assess disease frequency, risk factors at a particular time. can show dz prevalence

Question 2

case-control

Answer 2

compares a group with dz to group w/o dz, looks for prior event or risk factor. -> odds ratio

Question 3

cohort

Answer 3

prospective or retrospective. compares a group with a risk factor/exposure to a group without to see if exposure is associated with incr. dz prevalence. -> relative risk

Question 4

twin concordance

Answer 4

compares frequency of monozygotic and dizygotic twins developing same dz. -> heritability vs. environmental factors

Question 5

adoption study

Answer 5

compares siblings raised by biological vs. adoptive parents. -> heritability vs. environmental factors

Question 6

phase I trial

Answer 6

small n of healthy volunteers. -> safety, toxicity, pharmacokinetics, pharmacodynamics

Question 7

phase II trial

Answer 7

small n of pts w/dz. -> treatment efficacy, optimal dosing, adverse effects

Question 8

phase III trial

Answer 8

large n of pts, randomly assigned to tx vs. placebo. -> compares tx to standard of care

Question 9

phase IV trial

Answer 9

postmarketing surveillance of pts after tx is approved. detects rare or long-term adverse effects.

Question 10

sensitivity

Answer 10

= true positive rate. important for screening tests. = TP/(TP+FN) = 1-false neg rate. SN-N-OUT = highly sensitive, when negative, rules out dz

Question 11

specificity

Answer 11

= true negative rate. important for diagnostic tests. = TN/(TN+FP) = 1-false positive rate. SP-P-IN = highly specific, when positive, rules in dz

Question 12

positive predictive value

Answer 12

=proportion of positive results that are true positives. = TP/(TP+FP). PPV varies w/prevalence/pretest probability

Question 13

negative predictive value

Answer 13

=proportion of negative results that are true negatives = TN/(TN+FN). NPV varies inversely w/prevalence/pretest probability.

Question 14

incidence vs. prevalence

Answer 14

incidence = new cases (incidents). prevalence looks at all current cases. prevalence = incidence (almost) for short duration dz, e.g. common cold. prevalence + pretest probability (almost)

Question 15

odds ratio

Answer 15

case controls. odds that the dz group has target exposure divided by odds that dz free group was exposed

Question 16

relative risk

Answer 16

cohorts. risk of dz in exposed group divided by risk of dz in unexposed group.

Question 17

attributable risk

Answer 17

difference in risk vetween exposed and unexposed groups

Question 18

relative risk reduction

Answer 18

proportion of risk reduction attributable to intervention as compared to the control

Question 19

absolute risk reduction

Answer 19

difference in risk (not proportion) attributable to the intervention as compared to a control

Question 20

number needed to treat

Answer 20

number of patients who need to be treated for 1 patient to benefit = 1/ARR

Question 21

number needed to harm

Answer 21

number of patients who need to be exposed to a risk factor for 1 patient to be harmed = 1/AR

Question 22

type 1 error (alpha)

Answer 22

false positive error

Question 23

type 2 error (beta)

Answer 23

false negative error

Question 24

t test

Answer 24

compares mean of 2 groups

Question 25

ANOVA

Answer 25

compares means of more than 2 groups

Question 26

chi-square

Answer 26

compares 2 or more percentages or proportions of categorical outcomes, not means. chi-tegorical