Composite neuropsychological batteries and demographic correction: Standardization based on equivalent scores, with a review of published data

Equivalent Scores (ES; Capitani and Laiacona, 1988) is a 5-point scale that offers a solution to the problem of standardizing neuropsychological scores after adjustment for age and education, given that the common z- standardization is not generally applicable in these cases. ES are discussed, and their properties and limits are compared with those of z-standardization. In a battery of ES-standardized tests, the average ES (AES) for the whole battery can provide a measure of the overall cognitive level, free of the influence of age and education. We report empirical data from a battery composed of 10 ES-standardized tests, in order to discuss general properties of ES standardization. The expected mean of the AES is constant, regardless of the number or type of tests included. The standard deviation of the AES, however, is variable: it decreases in proportion to the number of tests, but increases in proportion to their intercorrelation. We provide general indications concerning the normality threshold, which are applicable to all batteries of ES-standardized tests regardless of the number and type.