HS300 equations

Prevalence

Number of cases at one point in time / total population

Cumulative incidence

(number of new cases / population at risk NOT including people who already had the disease/not susceptible)

Person-years

(# of people who have caught disease/dropped out) x (year)

Incidence rate

(number of new cases / total person-time/total person-years)

Crude mortality rate

(number of deaths in a given year / reference population)

Cause-specific mortality rate

(# of deaths from a specific disease or cause / population size) * 100,000

Proportional mortality ratio

(# of mortality due to a specific disease / total number of deaths in the same population) * 100

Birth rate

(# of live births within a given period / population of size at the middle of that period) * 1,000 population

Neonatal mortality rate

(# of infant deaths under 28 days of age / # of live births) * 1,000

Infant mortality rate

(# of infant deaths among infants aged 0-1 year / # of live births during the year) * 1,000 live births

Maternal mortality rate

(# of maternal deaths assigned to causes related to pregnancy / # of live births) * 100,000

Odds ratio

(A/B) / (C/D)

Incidence rate ratio

Incidence rate in treatment group / incidence rate in control group

Sensitivity

A / (A+C)

Specificity

D / (B+D)

Positive predictive value

A / (A+B)

Negative predictive value

D / (C+D)

Attack rate

(total cases / population at risk) * 100

Virulence rate

(# of severe cases / total cases) * 100

Case-fatality rate

(# of deaths / total cases) * 100

Attributable risk

(A / (A+B)) - (C / (C+D))

Attributable risk percent

(A / (A+B)) - (C / (C+D)), divided by A / (A+B) then multiplied by 100 to get a percent