Measures of association

Question 1

Formula for risk ratio

Answer 1

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

Question 2

Formula for odds ratio

Answer 2

[a/b]/[c/d]

Question 3

Interpretation for odds ratio

Answer 3

The odds of D+ among E+ are x times higher than for E-

Question 4

What are the odds of not having D+?

Answer 4

1/(OR of having D+)

Question 5

How do I find the OR of D+ if E-, if I have the OR of D+ if E+

Answer 5

e^(-ln(OR))

Question 6

95% CI of OR?

Answer 6

95% CI of ln(OR) = ln(OR) +/- 1.96 *sq(1/a + 1/b + 1/c + 1/d)
for the 95% CI of the OR, take e^

Question 7

Control Event Rate

Experimental Event Rate

Answer 7

c/c+d

a/a+b

Question 8

Relative Risk Reduction (RRR)

Answer 8

ARR/Control Event Rate

(Control Event Rate - Exp Event Rate)/Control Event Rate

Question 9

Absolute Risk Reduction (ARR)

Answer 9

Control Event Rate - Exp Event Rate

Question 10

Number Needed to Treat (NNT)

Answer 10

1/ARR = 1/(Control event rate - exp event rate)