per year rates

Some specific measures of disease occurrence are explained below:

  • Crude birth rate: Defined as the number of live births divided by the total population size.
  • Crude mortality rate: Calculated by dividing the number of deaths by the total population size.
  • Cause-specific mortality rate: Calculated by dividing the number of deaths from a particular disease by the total population size.
  • Case-fatality rate: Calculated by dividing the number of deaths from a specific disease by the number of people affected by the disease.
  • Standardized mortality ratio (SMR): Calculated by dividing the observed number of deaths by the expected number of deaths. This measure is used sometimes in occupational epidemiology. SMR of 2.0 indicates that the observed mortality in a particular group is twice as high as that in the general population.
  • Attack rate: An incidence measure typically used in infectious disease epidemiology. It is calculated by dividing the number of patients with disease by the total population at risk. For example, attack rate can be calculated for gastroenteritis among people who ate contaminated food.
  • Maternal mortality rate: Calculated by dividing the number of maternal deaths by the number of live births.

Standardized incidence ratio

The standardized incidence ratio (SIR) is a measure used to determine if the occurrence of cancer in a small population is high or low relative to an expected value derived from a larger comparison population. It is calculated by dividing observed cases (OC) by the expected cases (EC); the formula is SIR = OC / EC. EC is calculated based on age/sex-adjusted incidence rates of disease in a control population that is usually much larger (eg, population of the state). SIR = 1 implies that the observed incidence of cancer is equal to the expected value; SIR >1 implies a higher observed incidence than expected (eg, SIR = 1.5 means a 50% higher observed incidence).