Frequently Asked Questions

What is Prevalence?
chalkboard with a question mark drawn on it
  • “Prevalence” is the percentage of a population with a specific characteristic, such as domestic violence victimization, in a given time period.
    • Prevalence is calculated when there is information on the characteristics of the entire population of interest.
    • Prevalence is estimated when there is information on the characteristics of a sample of the population of interest.
  • Prevalence is generally determined by:
    • Randomly selecting a sample that is representative of the entire population.
    • For a simple representative sample, prevalence is the number of people in the sample with the characteristic of interest, divided by the total number of people in the sample.
Note. Adapted from National Institute of Mental Health. (n.d.). What is prevalence? Retrieved from https://www.nimh.nih.gov/health/statistics/prevalence/index.shtml
How is Prevalence Reported?
  • Prevalence is usually expressed as a percentage (e.g., 5 percent, or 5 people out of 100), or as the number of cases per 10,000 or 100,000 people, depending on how common the characteristic is in the population.
  • There are several ways to measure and report prevalence, which vary according to the timeframe for the estimate:
    • Point prevalence is the proportion of a population that has the characteristic at a specific point in time.
    • Period prevalence is the proportion of a population that has the characteristic at any point during a given time period of interest. The past 12 months is a commonly used timeframe.
    • Lifetime prevalence is the proportion of a population who, at some point in life, has ever had the characteristic.
Note. Adapted from National Institute of Mental Health. (n.d.). What is prevalence? Retrieved from https://www.nimh.nih.gov/health/statistics/prevalence/index.shtml
How is Prevalence Different from Incidence?
  • Incidence is a measure of the number of new cases of a characteristic, such as domestic violence victimization, that arise in a population over a given period (e.g., a month, a year, etc.); prevalence is the proportion of a population who have (or had) a specific characteristic in a given time period, regardless of when they first acquired the characteristic.
Note. Adapted from National Institute of Mental Health. (n.d.). What is prevalence? Retrieved from https://www.nimh.nih.gov/health/statistics/prevalence/index.shtml
What Else Do I Need to Know about Prevalence?
  • A variety of surveys and data systems are used to produce prevalence estimates of the existence of domestic violence in child protection and custody cases. Integrating information from multiple data sources can provide useful information about the presence of domestic violence in the populations of interest.
  • When examining prevalence estimates generated in a variety of surveys, it is important to take into consideration survey methodology differences that may impact the prevalence estimates produced.
    • The goals and approaches for various sources of domestic violence data are often different, making direct comparisons between them difficult.
    • Some methodological differences that may affect comparisons between studies include: the populations covered; the timing of data collection; sample design; mode of data collection; instruments and surveys used; operational definitions; and, estimation methods.
Note. Adapted from National Institute of Mental Health. (n.d.). What is prevalence? Retrieved from https://www.nimh.nih.gov/health/statistics/prevalence/index.shtml

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