When the researcher is satisfied with the individual items of a test, and reliability and validity are established at levels suitable to the intended purposes of the test, normative data is collected. Normative data is obtained by administering the test to a representative sample in order to establish norms. Norms are values that are representative of a group and that may be used as a baseline against which subsequently collected data is compared. Normative data helps get a sense of the distribution or prevalence of the characteristic being assessed in the larger population. By collecting normative data, various levels of test performance are established and raw scores from the test are translated into a common scale.
Common scales are created by transforming raw test scores into a common scale using various mathematical methods. Common scales allow comparison between different sets of scores and increase the amount of information a score communicates. For example, intelligence tests typically use a common scale in which 100 is the average score and standard deviation units are 15 or 16.