Epidemiology/ Biostatistics I

Question 1

What does a case-control study compare?

Answer 1

Group of people with a disease to group of people without; looks for prior exposure/ risk factor. (p.50)

Question 2

How are the results of a case-control study measured?

Answer 2

Odds Ratio (p.50)

Question 3

What does a cohort study compare?

Answer 3

Group with a given exposure/ risk factor to group without this exposure to see if exposure increases liklihood of disease (p.50)

Question 4

How are the results of a cohort study measured?

Answer 4

Relative Risk (p.50)

Question 5

How are the results of a cross sectional study measured?

Answer 5

Disease prevalance; causality is not established (p.50)

Question 6

What is sensitivity?

Answer 6

Proportion of all people with a disease who test positive; probability that the test detects a disease when it is present (p.51)

Question 7

How is sensitivity measured?

Answer 7

TP/ (TP + FN) or 1- false negative rate (p. 51)

Question 8

When are tests with high sensitivity most useful?

Answer 8

In screening for diseases with low prevalance (p.51)

Question 9

What is specificity?

Answer 9

Proportion of all people without the disease who test negative; probability that a test indicates non-disease when disease is absent (p.51)

Question 10

How is specificity measured?

Answer 10

TN/ (TN + FP) or 1- false positive rate (p.51)

Question 11

When are tests with high specificity most useful?

Answer 11

As confirmatory tests after a positive screening test (ex. HIV testing) (p.51)

Question 12

What can Positive Predictive Value measure?

Answer 12

Probability that a person actually has the disease given a positive test result (p.51)

Question 13

How is Positive Predictive Value measured?

Answer 13

TP/ (TP + FP); it varies with prevalance, the higher the prevalance the higher the PPV

Question 14

What can Negative Predictive Value measure?

Answer 14

Probability that a person actually is disease free given a negative test retult (p.51)

Question 15

How is Negative Predictive Value measured?

Answer 15

TN/ (FN + TN); varies inversely with prevalance, high prevalance yields low NPV

Question 16

What is an odds ratio?

Answer 16

Used in case control studies; 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; in 2x2 square odds ratio = (a/c)/(b/d) (p.52)

Question 17

What is relative risk?

Answer 17

Used in cohort studies to determine risk of developing the disease in the exposed group divided by risk in the unexposed group; in 2x2 square: RR= (a/(a+b)/(c/(c+d)) (p.52)

Question 18

What is attributable risk?

Answer 18

The difference in risk between exposed and unexposed groups; the proportion of disease occurances atrributable to the exposure; in 2x2 table AR= (a/(a+b))- (c/(c+d)) (p.52)

Question 19

What is absolute risk reduction?

Answer 19

Absolute resuction of risk associated with a treatment compared to a control (p.52)

Question 20

How do you calculate Number Needed to Treat?

Answer 20

1/ absolute risk reduction (p.52)

Question 21

How do you calculate Number Needed to Harm

Answer 21

1/ attributable risk (p.52)