Incidence rate describes the percentage of people in a study population who meet the eligibility criteria for a research project. In market research, this metric affects recruitment feasibility, sample delivery timelines, the selection of respondent sources and data-collection costs.
A high incidence rate means that the target group is relatively easy to find. A low rate, in contrast, indicates that many people must pass through screening before they can be qualified for the study.
What is incidence rate?
Incidence rate, often abbreviated as IR, is a metric showing the share of people who meet specified criteria among all people who undergo screening. In the context of incidence rate market research, it primarily refers to the availability of suitable respondents in a population, research panel, contact database or website traffic directed to a survey.
In practice, incidence rate is calculated as the ratio of qualified respondents to the number of people who completed the screening questions. Eligibility criteria may concern, among other things:
- demographic characteristics, such as age, place of residence or employment status,
- purchasing behaviour, for example use of a particular product category,
- ownership of a product or service,
- a decision-making role within a company,
- the frequency of specific activities,
- brand awareness, experience with a sales channel or exposure to a campaign.
If a project concerns all adult consumers, the share of eligible people may be high. However, if a study includes people responsible for purchasing specialised technologies in businesses with a specific profile, the incidence rate is usually low. This does not result from sample quality, but from the limited size of a precisely defined group within the available population.
The metric should be interpreted in relation to the defined research universe. The same person may qualify for one project and not qualify for another. Incidence rate therefore does not describe a permanent characteristic of a respondent or the market as a whole, but the relationship between screener criteria and the source from which recruitment is conducted.
Using incidence rate in practice
Incidence rate is used primarily at the planning and pricing stage of quantitative research. It helps estimate how many contacts, invitations or screening interviews will be required to obtain the planned number of complete, valid surveys.
In B2C projects, the metric is used, among other things, in studies of premium-product users, buyers of a specific category, people using financial apps or customers of particular retail chains. In B2B projects, incidence rate is particularly important in research involving decision-makers, technical specialists, representatives of narrow industries and companies that meet several conditions at once, for example relating to size, sector and technology use.
Before fieldwork begins, the rate may be estimated based on previous projects, panel data, client information, market analyses or a pilot study. The most reliable estimate, however, comes from a recruitment test conducted using a respondent source similar to the source planned for the main study.
In practice, incidence rate helps inform decisions concerning:
- a realistic sample size and fieldwork timeline,
- the selection of a panel, owned database, telephone recruitment, online campaign or face-to-face contact,
- the scope of screening questions,
- combining several recruitment sources,
- the design of quotas and rules for closing them,
- assessment of the risk of failing to achieve the target sample.
In mixed-methods research, the metric can support planning for both a quantitative survey and recruitment for in-depth interviews, focus groups or research diaries. In qualitative research, a low incidence rate does not rule out a project, but it usually requires a longer recruitment process, more precise screening and appropriately planned participant incentives.
How incidence rate affects survey cost
The relationship described as how incidence rate affects survey cost is direct: the lower the incidence rate, the greater the recruitment effort required to obtain one completed survey. Each person who does not meet the eligibility criteria generates a cost of contact, invitation, screening administration or purchasing a contact, even though they do not contribute to the final sample.
A low incidence rate can increase research costs for several reasons. More potential respondents must be reached, fieldwork takes longer, and available sources may more quickly exhaust suitable profiles. In B2B research, an additional factor can be the difficulty of reaching people with genuine knowledge or decision-making authority.
Costs should not, however, be analysed solely through the qualification rate. Survey length, question difficulty, respondents’ likelihood of responding to invitations, required quotas, research location, recruitment channel and the need to verify claimed characteristics also matter. A high incidence rate does not automatically guarantee low costs if the group is difficult to reach or requires multi-stage identity verification.
Rational cost management involves designing criteria that are methodologically justified but do not exclude respondents unnecessarily. It is also worth separating criteria that are essential to the research objective from characteristics that can be controlled later through quotas, data weighting or segment analysis.
Incidence rate and related methods
Incidence rate is related to many concepts used in research design, but it should not be confused with them. First of all, how does it differ from response rate? Response rate generally measures the proportion of eligible sampled people who complete a survey, relative to those invited or selected for participation. Incidence rate, by contrast, measures the proportion of people who qualify among those who have undergone screening.
The metric should also be distinguished from completion rate. The latter describes the proportion of people who begin a survey and complete it. A respondent may qualify for a study but not complete it, for example because of questionnaire length, technical problems or withdrawal during the interview.
Incidence rate is closely related to screening, meaning the set of qualifying questions. Screening identifies respondents who belong to the target group, while IR measures the proportion of that group within the selected recruitment source. Changing the wording of a screening question, the definition of a user or the reference period can substantially change the result.
In quantitative projects, the metric supports planning of sampling, quotas and data weighting. In qualitative research, it is useful for assessing the feasibility of recruitment for individual interviews and focus groups. In market analysis, it can also indicate whether the assumed group is sufficiently large and accessible to conduct primary research of the required quality.
For reliable results, incidence rate should be monitored separately for key segments and recruitment channels. An average rate can mask a situation in which one target group is easily accessible while another remains underrepresented. Such a diagnosis makes it possible to adjust respondent sources, timelines and data-quality control procedures accordingly.