An index is a measure that quantifies the degree of difference of a target’s attributes compared to a Benchmark.
If the percentage of the target attribute is exactly the same as the benchmark it is represented by 100 – all things are equal.
Any number above 100 represents how much the target attribute is above average (proportionally more in your file relative to the benchmark you chose). We say something is over-indexed.
Any number below 100 represents how much the target attribute is below the benchmark. We say something is under-indexed.
Another way to interpret and index is the number of times a characteristic appears in your file relative to the benchmark. For example, your File indexes 200 for kids aged 4 and under compared to BC. This means that households with kids 4 and under are 2 times more likely to be in your file than in the market.