Formulae

Question 1

Relative Risk

Answer 1

Incidence of exposed/incidence of unexposed

A/(a+b))/(c/(c+d)

Question 2

Attributable risk

Answer 2

Incidence exposed - incidence unexposed (/100)

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

Question 3

Odds ratio

Answer 3

Odds cases / odds controls

AD/BC

Question 4

P-values

Answer 4

P<0.05 statistically significant

P>0.05 results due to chance

Question 5

Confidence intervals

Answer 5

If value within 95% confidence intervals result not due to chance

Question 6

Incidence

Answer 6

No. of new cases in a time period in a population / no. of disease free at the start of time period

Question 7

Prevalence

Answer 7

No. cases in population / no. people in population

Question 8

Mortality

Answer 8

Deaths in given time periods due to a disease / population at start of time period

Question 9

Standardised mortality ratio

Answer 9

No. of observed deaths / no. of expected deaths

Question 10

Experimental event rate (EER)

Answer 10

Incidence in intervention arm

Question 11

Control event rate (CER)

Answer 11

Incidence in control arm

Question 12

Relative risk

Answer 12

EER/CER

Question 13

Relative reduction

Answer 13

(CER -EER)/CER

Question 14

Absolute risk reduction (ARR)

Answer 14

CER - EER

Question 15

Number needed to treat (NNT)

Answer 15

1/ARR

Question 16

Sensitivity

Answer 16

ID true positives

a/(a+c)

Question 17

Specificity

Answer 17

exclude true -ves

d/(b+d)

Question 18

Positive predictive value

Answer 18

Proportion of true +ve test results

a/(a+b)

Question 19

Negative predictive value

Answer 19

Proportion of true negatives

d/(c+d)