Spearman's Law of Diminishing Returns: Considering Data Skewness as a Psychometric Confound
Dixon. Hayley. Dissertation. 2011.doc (4.813Mb)
MetadataShow full item record
Spearman’s “Law of Diminishing Returns” (SLODR) states that the inter-correlations between subtests in a cognitive ability battery are higher in lower ability groups than in higher ability groups. A plethora of previous research has focused on the influence of test design upon the overall confirmation of SLODR, yet the relation between the skew of the data collected and the magnitude of SLODR found has been given little consideration. The present study investigates this relation in a dataset derived from the Minnesota Study of Twins Reared Apart. Traditional SLODR methodology is employed; alongside a new method for testing SLODR coined the Ability-Variability correlational method. The results found indicate a substantial positive relation between both the skew of the selection test and the magnitude of SLODR observed and furthermore between the skew of the entire cognitive ability battery and the magnitude of SLODR observed. In light of the present findings, it is recommended that data skewness should be acknowledged as a confounding variable when testing SLODR.