In the world of online quantitative market research, you cannot talk about surveys and online sample without discussing survey specifications like sample size, length of interview, and incidence rate (IR). All of these specifications impact sample cost in their own way, but incidence rate is the one that can cause the widest fluctuations and is the hardest to control.
The incidence rate is defined as the number of people who meet your specific criteria and would be eligible for your survey. Another way to think about it is that the incidence rate is the rate at which a specific characteristic, action, or behavior occurs in a population.
In the online sample world, the incidence rate is the percentage of respondents that meet the studies’ criteria and would be eligible to take the survey.
An example of this would be if you have 100 people, and you are looking for dog owners. In your pool (or sample) of 100 people, if 8 have dogs, then your incidence rate would be 8%. There are actually two different incidence rates in market research.
Calculating the incidence rate follows the same formula, whether you are calculating predicted or actual incidence rate. Here is the formula to use:
Number of people who meet specific criteria / Target Population
Here is an example of calculating the incidence rate for Ford employees in the overall auto industry:
Number of EV owners / Car Owners = EV Incidence Rate
186,000 / 2,000,000 = 9.3%
In a perfect world, we would have 100% incidence rate for every target audience market researchers are looking to gather insights from. But that is not the case. Incidence rates vary greatly depending on the targeting criteria and target audience you are trying to reach.
There are 2 critical factors that incidence rate directly impacts.
Incidence rate is a key driver of audience feasibility. Incidence rate allows panel providers to provide estimates on the number of respondents in their panel that would qualify for a particular study. The lower the incidence, the lower the feasibility, and the inverse applies as well.
Incidence is probably the most critical factor in sample pricing. The incidence rate drives the feasibility panel providers have for your target audience. The lower the incidence rate, the higher the cost of the sample since the respondents who match your criteria are much rarer than studies who are looking for a target audience with a higher incidence rate.
If you are trying to survey people who only live in Ohio, have your panel partner only send to respondents in their panel that have been profiled living in Ohio. This removes the need to send survey invites to a bunch of people you know will not qualify; it will increase the respondent experience of those who do qualify and increases the overall IR of your study.
If you are trying to ensure representation in your study by included quotas, try to have flexibility around what those quotas are. Some quota groups can have lower incidence rates than others and could potentially cause the overall IR to decrease.
There are times you may want to relax your audience screening criteria, especially if you know your ideal target audience is a difficult one to reach. This could include increasing the length of time you are looking at for a particular purchase, increasing a geographic scope, or much more.