C1M3

• Prevalence Rate


  A proportion, not a rate. The proportion of persons with a defined disease/condition at the time of the study. Can be applied to risk factors, to knowledge, to diseases/conditions.
• Incidence Rate


  The number of new events per person-time (e.g. of person-time is person-months, person-years). Useful for diseases occurring >1x in a person during the study period.
• Uses of Rates: When Comparing Data

  • Comparing observed rate (or risk) with a target rate (or risk)
  • Comparing 2 different populations (e.g. countries, regions, ethnic groups, control vs treatment group) at the same time
  • Comparing the same population but at different times
• 3 Broad Categories of Rates

  • Crude
  • Specific
  • Standardized
• Crude Rates


  Applies to entire populations without reference to individual components of the population
• Specific Rates

  Population is divided into subgroups based on a common characteristic
• Standardized Rates

  "Adjusted rates", are modified crude rates controlling for effects of age or other characteristic in order to allow for valid conclusions to be made
• Standardization of Rates

  1. Direct Standardization

  2. Indirect Standardization
• Direct Standardization


  Most common; removes effects of different age structures. ASDRs from each group are multiplied by the number of persons in that age group. Standardized rates are fictitious, as it only allows for investigators to make a fair comparison of rates between populations.
• Indirect Standardization


  Used if ASDRs are not available, and if the population to standardize is small. Assumes that your given population has the same death rates as the chosen standard population. Makes use of "standard rates" and applying them to your known age groups in order for your values to be standardized.
• Cause-specific rates are risky to compare as differences in diagnostic standards, in availability of health services, etc. makes conclusions invalid. They are rarely accurate enough for studying causal factors but are useful for studying trends in the causes of deaths over time and in knowing the relative importance of different disease groups.
• Maternal & Child Health Rates

  • Live Birth
  • Fetal Death
  • Infant Death
• Live Birth


  Delivery of a product of conception that shows any sign of life (breathing, crying, movement, pulse on the infant or on the umbilical cord, or heartbeat), after complete removal from the mother.
• Fetal Death

  • Early - death <20 weeks age of gestation, known as a miscarriage
  • Immediate - death between 20 to <28 weeks AOG
  • Late - death between 28 weeks AOG until birth, known as stillbirth
• Infant Death

  • Neonatal Death - death before the 28th day of life
  • Postnatal Death - death from the 28th day of life until before his/her 1st birthday
  • Perinatal Death - computed using the Perinatal Mortality Rate (stillbirths + <7 days old)
• Perinatal Mortality Ratio

  Variation of the Perinatal Mortality Rate, with the denominator being the number of livebirths only.
• Hebdomadal Death

  Variation of the Perinatal Mortality Ratio, with the numerator being neonatal deaths instead of <7 days old.