epi/biostats

Question 1

Cross-sectional study

Answer 1

Design: collect data from group of people to assess frequency (and risk factors) of disease at one point in time

Measures disease prevalence; can not establish causality

Question 2

Case-control study

Answer 2

Design: Retrospective. Compare group of people w/ disease to group without disease. Look at prior exposure/risk factor.

Measures odds ratio (OR)

Question 3

Cohort study

Answer 3

Design: Prospective or retrospective. Compare group with exposure to group without exposure and then look at difference in disease.

Measures relative risk (RR)

Question 4

Twin concordance study

Answer 4

Compare freq of both twins developing disease

Measures heritability and influence of environmental factors

Question 5

Adoption study

Answer 5

Compares siblings raised by biological vs adoptive parents -> measures heritability and environmental influence

Question 6

Ecological study

Answer 6

Analyzes populations instead of individuals for disease prevalance or risk factors etc

Question 7

Sensitivity

Answer 7

True (+) rate -> probability the test detects disease when it is present
= (test+ w/disease)/(all with disease)
=TP/(TP+FN)

Rules OUT disease and indicates LOW FN

Used for screening

Question 8

Specificity

Answer 8

True (-) rate -> probability negative result when disease not present
=(test- w/out disease)/(all without disease)
=(TN/TN+FP)

Rules IN disease and indicates LOW FP

Used for confirmation after screening

Question 9

Positive predictive value (PPV)

Answer 9

PPV= TP/ (TP+FP)

Varies directly with prevalence or pretest probability

Question 10

Negative predictive value (NPV)

Answer 10

NPV= TN/(TN+FN)

Varies indirectly with prevalence or pretest probability

Question 11

Odds ratio

Answer 11

Used in case-control studies

Odds group w disease were exposed/ Odds group without disease were exposed

OR=(a/c)/(b/d)

a= +disease, +risk
b= -disease, +risk
c= +disease, -risk
d= -disease, -risk

Question 12

Relative risk

Answer 12

Used in cohort studies

Risk developing disease in exposed group/ risk of disease in unexposed groups

RR=[a/(a+b)]/[c/(c+d)]

= [(+disease and risk)/(all +risk)]/
[(+disease and -risk)/(all -risk)]

Question 13

Attributable risk

Answer 13

AR= difference in risk btwn exposed and unexposed

=(a/a+b) - (c/c+d)

Question 14

Relative risk reduction

Answer 14

proportion of risk reduction attributable to intervention

RRR=1-RR

Question 15

Absolute risk reduction

Answer 15

ARR= difference in risk attributable to intervention = -AR= (c/c+d) - (a/a+b)

Question 16

Number needed to treat (NNT)

Answer 16

NNT=1/ARR

Question 17

Number needed to harm (NNH)

Answer 17

NNH=1/AR

Question 18

Precision

Answer 18

random error decreases precision

Increased precision-> decreased std and increased statistical power (1-beta)

Question 19

Accuracy

Answer 19

systemic error or bias decreases accuracy

Question 20

Berkson bias

Answer 20

study pop. selected from hospital is less healthy than general pop.

Question 21

recall bias

Answer 21

awareness of disorder alters recall by subjects. common in retrospective studies

Question 22

procedure bias

Answer 22

subjects in different groups treated differently

Question 23

Hawthorne effect

Answer 23

observer effect - modify behavior in response to awareness of being observed

Question 24

confounding bias

Answer 24

factor is related to both exposure and outcome but not on causal pathway-> distorts or confuses effect of exposure on outcome

Question 25

normal distribution

Answer 25

w/in 1 std= 68%
w/in 2 std=95%
w/in 3 std= 99.7%

Question 26

power

Answer 26

1-beta;
beta=type2 error: stating no difference when there is a difference

Increase power and decrease beta:

• Increased sample size
• Increased expected effect size
• Increased precision of measurement

Question 27

t-test

Answer 27

check difference btwn means of 2 groups

ex: mean BP btwn men and women

Question 28

ANOVA

Answer 28

check differences btwn means of 3 or more groups

ex: mean BP btwn multiple ethnic groups

Question 29

chi-square test

Answer 29

check differences between 2 or more categorical outcomes (not mean values)

Ex: comparing percentage of members of different ethnic groups who have essential HTN