Use the Audience Affinity Index tab (index where 100 = population average) to compare how concentrated your brand’s audience is within a target group versus the overall population.
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Affinity Index Formula
The following formula is used to calculate the Audience Affinity Index (an index where 100 = average vs. the population).
AI = \frac{(B_t / B_a)}{(P_t / P_a)} \times 100Variables:
- AI is the Affinity Index (index where 100 = population average)
- Bt is the brand audience in the target group
- Ba is the brand total audience
- Pt is the target group size in the population
- Pa is the total population size
To calculate the Affinity Index, compute the brand’s share that is in the target group (Bt/Ba) and divide it by the population share that is in the target group (Pt/Pa). Multiply by 100 to express the result as an index where 100 means the target group is represented at the same rate as in the population.
Related metric (Engagement tab): the Engagement (AI %) tab uses AI% = (N/T) × 100, where N is total engagements/interactions and T is reach/views/impressions. This is an engagement rate-style percentage, not the 100-based audience affinity index above.
What is an Affinity Index?
An Audience Affinity Index (sometimes called an index or composition index) is a marketing/media metric that shows whether a specific target group is over-represented or under-represented in a brand’s audience compared with the overall population. It is computed as a ratio of two shares (brand audience share ÷ population share) and scaled so that 100 means “average”. Values above 100 indicate the target group is more concentrated in the brand’s audience than in the population, and values below 100 indicate the target group is less concentrated.
How to Calculate Affinity Index?
The following steps outline how to calculate the Affinity Index.
- First, determine the number of people in your brand audience who are in the target group (Bt).
- Next, determine your brand total audience size (Ba).
- Next, determine the target group size in the overall population (Pt) and the total population size (Pa).
- Next, gather the formula from above: AI = ((Bt/Ba) / (Pt/Pa)) × 100.
- Finally, calculate the Affinity Index and (optionally) check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
brand audience in the target group (Bt) = 300
brand total audience (Ba) = 1000
target group size in population (Pt) = 200
total population size (Pa) = 1000
Affinity Index: AI = ((300/1000) / (200/1000)) × 100 = (0.30 / 0.20) × 100 = 150.
