What is an index?

A score that tells the user how much more or less likely a given population is to `agree` with a variable relative to the average. The penetration score of the cell (e.g. 15-24s) is compared to the penetration score of the base (e.g. all adults). If the score for 15-24s is the same as the score for all adults, the index will be 100. If 15-24s score higher than all adults, the index will be over 100; if they score lower, the index will be below 100.

Reading an index

The score is always relative to 100 (the average for the base or universe). If Irish 15-24s index 235 against Red Bull on a base of all adults, it means they are 135% more likely to use the brand relative to the average adult. In other words, 15-24s are more than twice as likely to drink Red Bull. If 55-64s index 24 against Red Bull, it means they are 76% less likely to use the brand relative to the average.

Indices should always be considered in conjunction with the other elements of a cell (e.g. sample, %). Exceptionally high or low index scores could be a result of low sample size. To ensure sufficient margin for error, only values above 120 or below 80 should be taken as evidence of a positive or negative correlation. Values in the range 80-120 should be considered average.