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Epidemiology UNF: Formulas

Just Formulas
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Cumulative Incidence
# new cases of dis during spec time period
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# of individuals at risk at start of period
Incidence Rate
# of new cases of dis during spec time period
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Person-time of observation among people at risk during same period
Period Prevalence
# of diseased in pop over a spec period
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Total pop at start (or midpoint) of spec period
Point Prevalence
# of diseased in pop at a spec time
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Tot pop at same spec time
Attack Rate
# of people who ate a certain food and became ill
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Total # people who ate that food
Case Fatality Rate
# people dying of dis during spec period after onset
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Total # with dis
Mortality Rate
Tot # of deaths from all (or spec) causes in one year
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Tot # of deaths in pop at midyear
SMR: Standardized Mortality (morbidity) Ratio
Observed # deaths (cases) per year
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Expected # of deaths (cases) per year
Relative Risk
a/(a+b)
---------
c/(c+d)
Odds Ratio
a/c ad
--- = ----
b/d bc
Attributable Risk
Risk in exposed - Risk in unexposed
Attributable Risk
(a/(a+b)) - (c/(c+d))
AR (Population)
((a+c)/N) - (c/(c+d))
AR Fraction
Risk in the exposed - Risk in the unexposed
----------------------------
Risk in the exposed
AR Percent (Population)
Risk in the population - Risk in the unexposed
----------------------------
Risk in the population
Death Rate
# deaths divided / tot person-time
Sensitivity
a/(a+c)
Specificity
d/(b+d)
Pos Predictive Value
a/(a+b)
Neg Predictive Value
d/(c+d)
Who's gonna rock these formulas?
You are!