Index

Index is a measurement that is commonly used in media to compare the composition (percentage) of a target audience on a media vehicle (TV station, application, radio station, website, newspaper, magazine, etc.) to a base audience. Indexes provide a quick comparison of the density of a target audience on media vehicles that are being compared to one another.

Example 1
This example compares the composition of men 25-54 on the XYZ website (our target audience) to the composition of men 25-54 in the online population (our base audience):

• The composition of men 25-54 visiting the XYZ website is 48%.
• The composition  of men 25-54 in the online population is 24%.

The index of men 25-54 on the XYZ website compared to men 25-54 in the online population is 200.

The index was derived by dividing the composition of the target audience (48%) by the composition of the base audience (24%).  

48% divided by 24% = 2, which is expressed as 200.

The index of 200 means that the percentage of men 25-54 on the XYZ website is 2 times higher than the percentage of men in the online population, or above average, compared to the base audience.

Example 2
Suppose that the percentage of men 25-54 on the XYZ website is 24% instead of 48%, and the percentage of men 25-54 in the online population remains at 24%.

24% divided by 24% = 1, which is expressed as 100. An index of 100 means that the percentage of men in the target audience is the same, or average, compared to the base audience. 

Example 3
If the percentage of men 25-54 on the XYZ website is 12%, and the percentage of men 25-54 in the online population is 24% then the index is .5, which is expressed as 50.  An index of 50 means that the composition of men 25-54 on the XYZ website is 50% less, or below average, compared to the percentage of men 25-54 in the base audience.

More on Interpreting Indexes
An index of 100 means the composition is the same in the target audience and the base audience.

Any index that is over 100, such as 110, means that the target audience composition is higher than the average or norm for the base audience. An index of 110 means that the composition of the target audience is 10% higher than the average/norm for the base audience. The higher the index, the more 'efficient' the target audience.  For example, ABC Website has an index of 110 compared to XYZ website with an index of 245. ABC Website is less efficient than XYZ Website because their index of 110 is significantly less than the index of 245.

An index that is below 100 means that the target audience composition is lower than the average or norm for the base audience.   A 90 index means that the composition of the target audience is 10% below the national average/norm of the base audience. 

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