The DTLA-4 was normed on 1,350 students from 37 states. The demographic characteristics of the normative sample are representative of the U.S. population as a whole (as reported in the Statistical Abstract of the United States, U.S. Bureau of the Census, 1996) with regard to ethnicity, race, gender, urban/rural residence, family income, educational attainment of parents, and geographic distribution. The norms of the DTLA-4 are stratified by age.
Reliability of the DTLA-4 was examined using estimates of contest sampling, time sampling, and scorer differences. Internal consistency reliability coefficients (content sampling) generally exceed .80 for the subtests and .90 for the composites. Time sampling was investigated using the test-retest technique. Test-retest coefficients range from .71 to .96 for the subtests; those for the composites all exceed .90. Scorer reliability coefficients were all in the .90s.
Evidence of the validity of DTLA-4 test scores is provided for content-description validity, criterion-prediction validity, and construct-identification validity. Content-description validity is demonstrated through careful documentation of subtest and item selection and analysis. A particularly powerful method for content-description validity is the use of conventional item analysis procedures, which allow the identification of good items and the deletion of bad items. Criterion-prediction validity is explored by comparing the results of DTLA-4 with those of other aptitude tests, such as the TONI-3, WISC, KABC, PPVT, and W-JPEB. Construction-identification validity is demonstrated by showing the relationship between DTLA-4, chronological age and tests of academic achievement. Further, DTLA-4 subtests and composites intercorrelate and factor according to hypothesized constructs. Convincing evidence for validity is provided in the form of several confirmatory factor analyses.
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Donald D. Hammill
Donald D. Hammill received his doctorate in educational psychology-special education from the University of Texas at Austin in 1963. He had previously served as a teacher in the Corpus Christi (Texas) public schools and as a speech and language therapist in the Deer Park (Texas) public schools. He earned a certificate of clinical competence from the American Speech and Hearing Association in 1963. From 1963 to 1965, he held an assistant research professorship at the Institute of Logopedics at Wichita State University in Kansas, where he studied the language problems of children with brain damage. In 1965 he went to Temple University in Philadelphia, where he became professor of special education. He resigned from Temple in 1972 in order to return home to Texas.
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