In market research, incidence rate (IR) refers to the proportion of individuals in a population who meet the inclusion criteria for a study. This is typically relevant in the context of surveys or other research methods that involve recruiting respondents for a study from a larger population.

For example, if a study is looking to survey individuals who own a particular product, the incidence rate would be the percentage of people who meet that criteria divided by the total sample pool. If the total sample pool is N=1,000 individuals, and N=600 own that product, the incidence rate would be 60%.

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If your survey is targeted to a general population, the incidence rate is 100% because everyone qualifies to take the survey.

‍Let’s work out a real example

Let’s say you want to send out a survey targeting women aged 25-49 years in Singapore. To calculate the incidence rate for this group, you will need to know the total number of women in the specified age group and divide it by the total population of Singapore.

To get this data, I pulled out the below table from Singapore’s Department of Statistics (DOS). The table shows Singapore’s resident population by Age Group and Sex (Source : Census of Population 2020).

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From the above table, I pulled out the number of women who fall into each of the age brackets (25-29, 30-34, 35-39, 40-44, and 45-49 years) and added them up. The total number of women in the age group 25-49 years is N = 774,089.

I then divide this number by the total population, which in this case is the total resident population of Singapore, N = 4,044210.

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774, 089 / 4,044210 = 0.19. Which means the Incident rate of women between the ages 25 - 49 years in Singapore is 19%. So, if I were to send out a survey to N = 1000 Singaporeans, I can expect about N = 190 women between the ages 25 - 49 years to qualify for the survey.

Incident rates may not always be easy to figure out

You may not always be able to calculate the IR on your own, either because of a lack of publicly available data or because the target group is highly specific or niche.

If you are a research buyer collaborating with a vendor such as a survey panel provider, they will typically provide you with an estimation of the IR in such scenarios. 

They estimate the IR either based on pre-collected information they have on their database of survey takers or by conducting an "incidence rate check" which is essentially a short survey run using a set of questions to determine what percentage of respondents meet the inclusion criteria. 

For example, to determine the IR of Singaporeans who bought a house in Central Singapore in the past 5 years, researchers could launch a quick survey to 100 respondents with 2-3 questions aimed at identifying the specific target group. Based on the survey responses, if 20 out of 100 respondents meet the inclusion criteria, the estimated incidence rate would be 20%. With this estimate you and the research provider can then get an idea of what sample size is feasible for your study.

This service is often provided at no cost or for a small fee. So, it's worth reaching out to your vendor to get a better understanding of how they can help with getting an idea of your audience size.

Importance of Incidence Rate

Understanding the incidence rate of your survey is crucial because it can impact the cost, feasibility, and timelines of your research study.

Broadly, incidence rates are divided into two categories

• High incidence rates : If a study has a high IR it means that a large proportion of the population for the survey meets the inclusion criteria and is therefore eligible to participate in the study.  This can lead to several benefits, including easier attainment of larger sample sizes such as N=1000, reduced costs, and a quicker completion time for the study.

• Low incidence rates : A low incidence rate indicates that only a small percentage of the population meets the inclusion criteria and is eligible to participate in the survey. This may require researchers to adjust their expectations regarding attainable sample sizes. For instance, surveys that target niche groups, such as CEOs of B2B companies, may require settling for smaller sample sizes, such as N=50 or N=100. Lower incidence rates can also increase the study's cost as one may have to reach out to a wider audience to achieve the desired sample size or offer incentives to boost participation rates. It can also stretch timelines for fieldwork, as you may have to keep the survey open for a wider time-frame to allow for niche respondents to trickle in.

Suggestions on improving incidence rates

Don’t let a low incidence rate discourage you. If you are partnering with a research vendor, don’t hesitate to reach out to them to tap into their expertise. Explore the below strategies to boost the IR or find alternative solutions. :

1. Consider broadening your audience by relaxing your criteria.

Here are some examples : 

• If you are interested in surveying those who purchased a product in the past 1 month, can this be relaxed to the past 2 months? Or 6 months? Give a think about how strict you need to be with your time frames.
• Same goes for frequency of purchase. Do you have to stick to consumers who buy your product every week or can you relax it to every month or every few months without compromising your insights?
• In the case of niche audiences like CEOs of B2B companies, consider relaxing the criteria to say perhaps anyone in a leadership or management role. You can even consider surveying employees who have some decision-making capacity, if relevant to your survey.
• If you want to understand what motivates consumers to buy niche products like electric vehicles, don't limit your survey to existing electric vehicle buyers. Instead, broaden your audience to also include those who are considering buying electric vehicles in the near future.

2. Pre-target your respondents

If you already have some pre-collected data on your target respondents who meet a specific criteria of your survey, you can exclusively target them instead of blasting the survey to a wider audience. Most survey panel providers have hundreds of pre-collected variables for each participant who joins their panel.

This approach can improve your chances of reaching your intended audience and reduce costs by avoiding the need to send the survey to a broad population and subsequently disqualify respondents who don't meet the criteria. If you wish to survey only women aged 25-49 years, and if you or your research provider has pre-collected demographic information on respondents, use this to target your surveys. 

3. Do away with quotas

When you have a high incidence rate, you typically apply quotas to ensure you get a representative split of different demographic segments (e.g., 50% male, 50% female). If your incidence rate is low, and the audience you are targeting is niche, consider relaxing the quotas to allow for a natural fallout of respondents, without enforcing quotas.

That's all for now! We hope you found this useful.

‍Feel free to check out more articles on concepts related to market research on our Learn Section.

If you have questions related to Milieu's survey platform and/or other product/service offerings feel free to reach out to sales@mili.eu.