Q: I appreciate the difference between percentile and percentage, but can you shed light on the difference between percentile and centile?

A: Ed Livingston, MD, a JAMA deputy editor and author of the statistics chapter in the 11th edition of our style manual, responds:

Percentile refers to the percentage below which a group of observations fall, ie, 93 percentile means that 93% of the observations fell below that value. If I had a score that was in the 85th percentile, I had a score that was better than 85% of all people taking that test.

Centile refers to which group an observation belongs to when the population is divided into 100 equal groups, like a quartile. With a quartile there are 4 equal-sized groups and with a centile there are 100 equal-sized groups—so in practice it’s the same as a percentile. —Cheryl Iverson, MA