The term norm group and 'comparison group' are used interchangeably. Norm groups are used for benchmarking, and are the best way to see how a score compares with the scores other people got.
A straightforward 'raw score' of say 16 out of 20 only tells us something if we know what other people got in the same test. Is 16 out of 20 a high score, a low, score, or about average for that test? We don't know until we can compare it with what other people got. We need a benchmark.
This is where percentile scores come in. They tell us the percent of scores which are lower than the score being considered. This is better understood with some examples...
For example: if a candidate scores in the 90th percentile, their score is higher than 90% of the scores achieved by other people in the norm group. In other words they are in the top 10%. A percentile score of the 50th percentile means 50% scored lower than the candidate and 50% scored higher; this score is exactly 'average' compared with the people in the norm group.
The norm group you choose is important so you can compare your candidates against a meaningful benchmark. You pick the norm group for each test when you setup our Project. Test Partnership has built many norm groups for you to choose from, such as for example Graduates, Apprentices, Managers and Executives, General Population...and so on.
What is a good score?
So now you understand about percentile scores and norm groups you will have a sense of what a good score is. Consider some examples:
Candidate A scores in the 56th percentile against a Graduate norm group. This means their score was higher than 56 of all the other graduates who have taken that test. That's not bad, in fact it's almost exactly average.
Candidate B scores in the 19th percentile against a General Population norm group. This means their score was in the bottom 19% of all the people who have taken that test. That's not great, but still better than 19% of people. Some employers consider the bottom 19% not to be good enough, so they could ask the candidate about their performance and possibly select them out of this round.
Candidate C scores in the 83rd percentile against a Managers norm group. This means their score is higher than 83% of other managers who have taken that test. That's very good and probably merits progressing them to the next round of selection.
We have another article here on how to interpret scores. And a video here.