Incidence rate refers to the frequency of something occurring within the population. The smaller the incidence rate, the more difficult it is to reach the audience. It is sometimes possible to estimate incidence rates based on existing data, but otherwise there are two methods used by quantitative researchers to find incidence rate:
- Ask a panel partner to run an incidence test among their respondent pool.
- Use your own survey’s data. This requires access to the number of completed responses and the number of screenouts (people who fail the screening question. The incidence rate can then be computed using the following formula:
- In a tracker study conducted by Pew, the results in 2015 showed that 68% of adults in the US owned a smartphone. This is a very high incidence rate, so if you conducted a survey targeting adult smartphone owners, they would be relatively easy to find. If you approached a random sample of 100 adults, 68 of them would own a smartphone.
- In this same tracker study, 19% of adults in the US owned an e-book reader. This is a much smaller incidence rate, so it would be more challenging and time-consuming to find e-book reader owners.
It is imperative to consider incidence rate when defining a target audience. The smaller the incidence rate, the more difficult it will be to find qualified respondents, the more expensive sampling costs will be, and the longer the survey will remain in field. For example:
- A director overseeing menu design at a fast food company wants to survey people who eat fast food, but she has a limited budget for the project and wants to move quickly. She could survey people who eat fast food several times per week, which has an incidence rate of 19%. However, this low incidence rate will make it difficult to complete the study with their tight budget and turnaround time.
- If she has flexible targeting parameters, she can solve this problem by surveying people who eat fast food at least once per week (47% IR) or once per month (80% IR). This will help her complete her project on time and on budget without sacrificing on insights.