The relationship between ipsatized and normative measures of personality

Recent interest in the use of ipsative personality instruments has focused on the questions of their reliability and their equivalence to normative measures (e.g. see Saville & Willson, 1991). A general expression is presented for computing the relationships between normative scales and ipsative ones derived from them, based on the number of scales and the intercorrelations between the normative scales. The results obtained from various empirical and computer generated data sets were compared with those expected on the basis of the equations and a close correspondence found. Expressions for computing the reliability of ipsatized scales and the reliability of ipsatized scale differences were also produced and the implications of these for profile analysis are discussed. It is noted that ipsatized measures are unreliable when the number of scales is less than about 10 or when the correlations between normative scales are greater than about .30. This unreliability is increased by full ipsatization (i.e. the equating of within-subject scale score variances) and by inequality of the variances of the normative scales from which the ipsatized scales are derived.