How to Convert Percentiles to Standard Scores

Percentiles are probably the most commonly quoted test score in education and indicate a student's ranking compared to a hypothetical group of 100 similar students of the same age, for the same test. Standard scores, however, allow us to compare a student's performance on different tests and among different groups of students. The ability to convert one score to another is therefore important to provide an accurate overview of progress and in the formation of a baseline assessment.

Instructions

1

Locate a score conversion table from the test administration book or, if this is unavailable, from websites such as Dumont Willis, MedFriendly or Docstoc.

2

Identify the columns listing percentile rank and standard scores.

3

Find the percentile rank, and then look across the chart, on the same line of data, to obtain the standard score equivalent.

For example:

75th percentile equates to a standard score of 110.

27th percentile equates to a standard score of 91.

6th percentile equates to a standard score of 77.