transformed scores I: percentiles

This chapter provides a definition of percentile and illustrates the computation of percentiles. The percentile rank corresponding to a given score refers to the percent of cases in a given reference group scoring at or below that score. A specified raw score may be converted to the corresponding percentile rank to express its standing relative to the reference group, or the raw score corresponding to a specified percentile may be determined. The percentile divides the scale into 100 equal parts; however, the decile divides the scale into 10 equal parts and the quartile divides the scale into four equal parts. The score corresponding to the 50th percentile has the unique property that exactly half the scores in the group are higher and exactly half the scores in the group are equal or lower. It is called the median and it is one of the measures of central tendency.