WIAT3 Tech Manual.pdf - CAMPBELA

42 Chapter 3Evidence Based on Relationships With Other VariablesExamining relationships between test scores and related external variables provides additional evidence ofa scale’s validity by providing important information regarding what a test measures and whether it behavesas expected. This evidence may be provided through an examination of the scale’s relationship to otherinstruments designed to measure the same or similar constructs and through an examination of testperformance criteria and group membership variables.The evidence of WIAT–III validity described in this section is divided into two parts. The first sectiondescribes a series of studies that were conducted concurrently with the scale’s standardization to examinethe relationship between WIAT–III test scores and measures of academic achievement and cognitiveability. The second section describes special group studies and provides evidence supporting the validity ofWIAT–III scores by investigating the performance of students in these special groups (i.e., students whoare academically gifted, students with mild intellectually disability, students with learning disabilities, andstudents with expressive language disorder).Relationships to Other MeasuresThe relationships between the WIAT–III and the following measures were examined: WIAT–II,WPPSI–III, WISC–IV, WAIS–IV, WNV, and DAS–II. There are a number of possible influences onthe validity coefficients and score differences between two instruments, many of which may also interactwith one another. Some of these influences are: (1) time interval between tests, (2) developmental changeor learning during the time interval, (3) structural differences between measures, (4) reliability of eachmeasure, (5) memory of test content from first administration, (6) differential procedural learning andpractice, and (7) motivation level of the student. These influences and their interactions with each othershould be considered when interpreting the results of the comparison studies reported in this section(Bracken, 1992; Zhu & Tulsky, 2000). Many of these issues are discussed in detail in Bracken (1992) orStrauss, Spreen, and Hunter (2000), and methods have been proposed to estimate the relative contributionof these factors (McArdle & Woodcock, 1997).Correlations With the WIAT–IIThe WIAT–III and the WIAT–II were administered in counterbalanced order to 140 students in gradesPK–12, with a testing interval between 1 and 30 days, and a mean testing interval of 9 days. Means,standard deviations, and correlation coefficients corrected for range restriction were calculated separatelyfor the portion of the sample taking each administration sequence and then averaged. This methodprevents practice effects from artificially lowering the correlation coefficients. Table 3.11 presents themeans, standard deviations, and corrected correlations, based on grade-based standard scores, for theWIAT–II and the WIAT–III subtests and composites.Copyright © 2009 NCS Pearson, Inc. Normative data copyright © 2009 NCS Pearson, Inc. All rights reserved.