Calculator 1: Calculate Actual Incidence Rate
Use this tool when you have completed fieldwork or a soft launch and need to determine the actual incidence rate based on screening data.
Interpretation: Out of every 100 people you invite, approximately 0 will qualify for your survey.
Calculator 2: Sample Size Feasibility
Use this tool for planning. Estimate how much traffic (sample) you need to purchase based on an estimated Incidence Rate.
To get 0 completes at a 0% IR, you must send invitations to at least this many people.
How to Calculate Incidence Rate in Market Research
In the field of market research, Incidence Rate (IR) is one of the most critical metrics affecting the feasibility, timeline, and cost of a study. Whether you are conducting a quantitative survey, a focus group, or an IDI (In-Depth Interview), understanding your IR is essential for budgeting and sampling.
What is Incidence Rate?
Incidence Rate represents the percentage of the general population (or a specific target list) that qualifies for your study based on your screening criteria. It essentially measures how "easy" or "hard" it is to find your target respondent.
- High Incidence (e.g., >50%): Broad targets, such as "Coffee Drinkers" or "People who own a smartphone." These studies are generally cheaper and faster to field.
- Low Incidence (e.g., <5%): Niche targets, such as "Decision makers in IT security" or "Owners of a specific model of luxury car." These studies require screening a massive number of people to find a few qualified respondents, increasing costs significantly.
The Incidence Rate Formula
To calculate the incidence rate after a study or a soft launch, use the following formula:
Variables:
- Qualified Respondents: The number of people who passed all screening questions.
- Total Respondents Screened: The total number of people who entered the survey and answered the screening questions (including those who were disqualified).
Example Calculation
Imagine you launch a survey about "Vegan Pet Food." You send the survey link to a general population panel.
- 2,000 people click the link and answer the screener (Total Screened).
- Only 100 people actually buy vegan pet food (Qualified).
Calculation: (100 / 2,000) × 100 = 5% IR.
This means for every 100 people you invite, only 5 will qualify. You need to account for this "waste" in your budget.
Why Incidence Rate Matters for Cost Per Interview (CPI)
Incidence rate is inversely related to the Cost Per Interview (CPI). Panel providers charge for the effort required to screen out non-qualified respondents.
If your IR is 1%, the panel provider must recruit and screen 100 people just to get you 1 complete. If your IR is 50%, they only need to screen 2 people to get 1 complete. Consequently, a lower IR results in a higher CPI and a longer time in the field.
How to Estimate Required Sample (Feasibility)
Before launching a study, you should estimate the IR to determine how many people you need to reach. The formula for feasibility is:
If you need 400 completes and you estimate a 20% IR, you calculate: 400 / 0.20 = 2,000. You must ensure your panel provider has access to at least 2,000 active members in that demographic to make the study feasible.
Tips for Managing Low Incidence Rates
- Broaden Screening Criteria: Can you accept "Decision Makers" generally rather than just "CEOs"? Loosening criteria increases IR.
- Use Targeted Lists: Instead of screening the general population (GenPop), start with a list of people known to possess the behavior (e.g., a list of car owners). This artificially increases the IR for your specific study.
- Shorten the LOI: If IR is low, respondents are rare. Do not lose them with a 30-minute survey. Keep the Length of Interview (LOI) short to maximize completion rates among the few who qualify.