Equations!

Question 1

Number needed to treat

Answer 1

NNT = 1/ARR (remember to round answer up to whole number)

Question 2

Absolute risk reduction

Answer 2

ARR = CER-EER

Question 3

Risk ratio

Answer 3

RR = EER/CER

Question 4

Control event rate

Answer 4

CER = outcome in controls/total number of controls

Question 5

Experimental event rate

Answer 5

EER = outcome in cases/total number of cases

Question 6

Relative risk ratio

Answer 6

RRR = CER-EER/CER

Question 7

Positive predictive value

Answer 7

PPV = true positive/all positives

Question 8

Negative predictive value

Answer 8

NPV = true negative/all negatives

Question 9

Sensitivity

Answer 9

True positive/true positive + false negative

Question 10

Specificity

Answer 10

True negative/false positive + true negative

Question 11

Positive likelihood ratio

Answer 11

LR+ = sensitivity/1-specificty

Question 12

Negative likelihood ratio

Answer 12

LR- = 1-sensitivity/specifity

Question 13

Interquartile range

Answer 13

IQR = median of upper 1/2 - median of lower 1/2

Question 14

Standard error of the mean

Answer 14

SEM = standard deviation/Sq root of no. of patients

Question 15

Odds ratio

Answer 15

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

Question 16

Prevalence = incidence x duration. True or False?

Answer 16

True

Question 17

Standard deviation

Answer 17

Sq root of variance

Question 18

Post test odds

Answer 18

LR X pretest odds

Pretest odds = prevalence

Question 19

False positive rate

Answer 19

1-specificity

Question 20

Population attributable risk

Answer 20

attributable risk x proportion of population exposed

Question 21

CIs for NNT (upper CI)

Answer 21

1/lower limit ARR CI

Question 22

CIs for NNT (lower CI)

Answer 22

1/higher limit for ARR CI

Question 23

Post test probability

Answer 23

Posttest odds / (Posttest odds + 1)

Question 24

Pretest odds

Answer 24

Pretest probability / (1 - Pretest probability)