Percentiles are not to be confused with percentages although the principles behind both of these are similar. In an assessment context, percentiles are a way of presenting percentages, but in comparison to the individuals who have completed the assessment previously rather than the total number of questions in the assessment.
Percentiles tell you how many individuals in the ‘norm’ or ‘comparison’ group an individual has performed better than. For example, an individual who achieves the 30th percentile is deemed to have done better than 30% of the individuals in the comparison group.
If a test consisting of 20 questions, which means a maximum possible score achievable is 20, is given to hundreds of individuals, from whom no one achieves a score greater than 15; then if a new candidate takes this test and achieves a score of 16, 17, 18, 19 or 20, they would be deemed to be at the 99th percentile, irrespective of which score above 15 they achieve. This is because they have done better than 99% of the comparison group.Using percentiles helps organisations select the best of ‘what’s available’.