Summary EPH2021 Formula Sheet

EPH2021 Formula sheet exam (page 1/2)


Measures of association

Two by two table
Cases Non-cases
Exposed a b
Non-exposed c d

Odds ratio (OR)
Exposure odds cases (a/(a+c))/(c/(a+c)) a/c a*d
OR = = = =
Exposure odds non-cases (b/(b+d))/(d/(b+d)) b/d b*c

Relative risk (RR)
I exposed a/(a+b) I: Incidence
RR = =
I non-exposed c/(c+d)

Attributable risk (AR)
AR = I exp – I non-exp
= (a/(a+b)) – (c/(c+d))

Attributable proportion (AP) among the exposed
I exp – I non-exp (a/(a+b)) – (c/(c+d))
AP exp = =
I exp (a/(a+b))

AP exp = (RR – 1)/RR

Attributable proportion (AP) in the total population
I tot – I non-exp ((a+c)/N) – (c/(c+d)) N=a+b+c+d
AP tot = =
I tot (a+c)/N

AP tot = (p(RR-1)) / (p(RR-1) +1) p: proportion of exposed individuals




See next page for formulas of measures of diagnostic accuracy and reliability