Ipsative Standardization is Essential in the Analysis of Serial Data

Paul R. Yarnold & Robert C. Soltysik

Optimal Data Analysis, LLC

An omnipresent experimental method in all quantitative scientific disciplines involves what is commonly called, for example, a time-series, repeated measures, clinical trial, test-retest, longitudinal, prospective, pre-post, AB, or, more generally, a serial design. In a serial design each observation is assessed on a measure on two or more test sessions spaced by a theoretically meaningful time span. This note presents a classic serial study with n=12 observations, each measured at the same four theoretically-significant times. Scatter plots illustrating test session and raw, normative, and ipsative standardized data demonstrate that ipsatively standardized data are clearly the most appropriate to statistically address fundamental questions that motivate such research.

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