Incidence Rate (IR or Incidence) in market research is the percentage of potential respondents that qualify for a study based upon the given screening qualifications. Simply defined, incidence is the frequency of something occurring in a given population, for example, x percent of adults in the United Stated chew gum. In the marketing research world, the incidence rate is used to measure the level of effort needed to reach respondents that are qualified to take a particular survey (pass the survey screeners).