Naked Statistics: Stripping the Dread from the Data

by Charles Wheelan

The benefit of these kinds of descriptive statistics is that they describe where a particular observation lies compared with everyone else. If I tell you that your child scored in the 3rd percentile on a reading comprehension test, you should know immediately that the family should be logging more time at the library. You don’t need to know anything about the test itself, or the number of questions that your child got correct. The percentile score provides a ranking of your child’s score relative to that of all the other test takers. If the test was easy, then most test takers will have a high number of answers correct, but your child will have fewer correct than most of the others. If the test was extremely difficult, then all the test takers will have a low number of correct answers, but your child’s score will be lower still.