How Is Percentile Calculated?
Definition The term “percentile” has no standard accepted definition, but anyone who has ever taken a standardized test has a general idea of what it means. It is a method of scaling a rank-ordered list of data, such as students’ SAT scores, into a zero to 100, or percentile, range. This works very well for large amounts of data, but can easily skew the interpretation of small data sets. Data Preparation If a data point is at the 75th percentile, that usually means the selected data point is greater than 75 percent of all the other data points. That makes the first step to calculating percentiles collecting and rank-ordering all of the data. Equation The easiest way to calculate percentiles is directly from the rank-order data. Once a percentile is associated with a rank number, the score or data point can then be used to define the percentile rank. The equation is: R = p(N +1) R = rank-order position (1, 2, 3…) N = total number of data points p = percentile rank in decimal form (i.e
