Snapshot There is a city with a population of 500,000. There are 20,000 women of childbearing age. In the year 2020, there are 20 maternal deaths and 200 live births. The maternal mortality rate is 20/200 = 0.1. Introduction Overview in addition to prevalence and incidence, there are other methods of measuring the occurrence of disease Crude mortality rate describes the total number of deaths per years per 1,000 people equation number of deaths/total population size Cause-specific mortality rate describes the mortality rate caused by a certain disease/cause e.g., aggressive malignancy equation number of deaths by a certain disease/total population size Case-fatality rate equation number of deaths by a certain disease/total population affected by the disease Attack rate a type of incidence measure that is usually used in the epidemiology of infectious disease e.g., gastrointestinal infection in patients caused by contaminated food equation number of patients with the disease/total population at risk Maternal mortality rate equation number of maternal deaths/number of live births Crude birth rate equation number of live births/total populations size Prospective and Retrospective StudiesProspective studiespatients enrolled before data collectionparticipants followed over timedata collected on exposures and outcomes as they ariseRetrospective studiesinvolve collecting historical information from a sample of patientsenrollment occurs after exposure and outcome have already occurredCase-Control StudyRetrospective (almost always)Compares patients with and without disease to asses their odds of a certain exposureOdds ratio (OR) is measure of disease associationOR= odds of exposure among cases/odds of exposure in non-cases = ad/bcodds of exposure among cases=# cases with exposure/# cases without exposure = a/codds of exposure among non-cases=# non-cases with exposure/# non-cases without exposure=b/d"How much more likely is it that patients with cirrhosis have been exposed to heavy alcohol use compared to controls?"Cohort StudyCan be eitherprospectiveorretrospectiveCompares groups with and without an exposure to assess associations with subsequent diseaseRelative risk (RR) is measure of disease associationRR= incidence rate in exposed group/incidence rate in unexposed group = [a/(a+b)]/[c/(c+d)]incidence rate in exposed group=# of exposed cases/(# total exposed cases and non-cases) = a/(a+b)incidence rate in unexposed group=# of unexposed cases/(# total unexposed cases and non-cases)=c/(c+d)"How much more likely are patients to develop cirrhosis if they are exposed to heavy alcohol use?"Cross-Sectional StudyExposure and outcome are assessed simultaneouslyAscertains association not causalityPrevalenceis measure of disease association"How much higher is the proportion of cirrhosis patients with heavy alcohol use compared to those without cirrhosis?"