· Ages: 6-0 through 17-0 Years
· Testing Time: 40 minutes-2 hours
The DTLA-4 is the oldest and most venerable of the tests of specific mental abilities. The test includes 10 subtests. The results of the subtests can be combined to form 16 composites that measure both general intelligence and discrete ability areas. The test permits interpretation in terms of current theories of intellect and important behavioural domains. The DTLA-4 is the test of choice for profession-als interested in a thorough investigation of a person's cognitive functions. This test not only measures basic abilities, but also shows the effects of language, attention, and motor abilities on test performance.
Statistical Characteristics of the DTLA-4
DTLA-4 was built with the American Psychological Association's standards for technical adequacy clearly in mind. The test was normed on 1,350 students residing in 37 states. The demographic character-istics 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 gender, race, ethnicity, urban/rural residence, family income, educational attainment of parents, and geographic distribution. Norms are stratified by age.
Three types of scores are available: percentiles, standard scores, and age equivalents. Percentiles provide the examiner with an index that is easily understood by parents and others with whom the test results are to be shared. Subtest standard scores are based on a distribution having a mean of 10 and standard deviation of 3. Composite standard scores, called quotients, are based on a distribution having a mean of 100 and standard deviation of 15. Age equivalents are indexes of relative standing that translate subtest raw scores to what are commonly termed "mental ages."
Reliability of DTLA-4 was investigated using estimates of content 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-identific-ation 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. Construct-identification validity is demonstrated by showing the relationship between DTLA-4 and chronological age and tests of academic achievement. Further, DTLA-4 subtests and composites intercorrelate and factor according to hypothesised constructs. Convincing evidence for validity is provided in the form of several confirmatory factor analyses.
Controlling for Test Bias
The DTLA-4 was built to minimise the effects of bias. Numerous steps were taken to detect and eliminate sources of cultural, gender, and racial bias. First, the effects of bias were controlled and minimised through the inclusion of minority and disability groups in the normative sample. Second, the examination of reliability and validity information was presented for all these subgroups. A particularly powerful element of content-description validity is the demonstration of excellent internal consistency reliability for the different racial, ethnic, and gender groups. Third, the use of differential item functioning analysis to reduce item bias during item selection. Delta score values were used to remove items that appeared to be biased against targeted groups. Finally, none of the subtests are timed.
Overall Composite. Because this composite is formed by combining standard scores of all 10 subtests in the battery, it is probably the best estimate of g.
Optimal Level Composite. Because this composite comprises the four highest standard scores made by the subject on the subtests, it is the best estimate of a person's overall "potential." In this context, potential means the highest level of performance that an individual is capable of when the inhibiting influences of his or her deficits are disregarded.
Domain Composites. Contrasting composites are provided for three domains: language, attention, and manual dexterity. DTLA-4 includes the following: Verbal Composite, Nonverbal Composite, Attention-Enhanced Composite, Attention-Reduced Composite, Motor-Enhanced Composite, and Motor-Reduced Composite.
Theoretical Composites. Subtests are easily assigned to composites that represent major popular theories. Thus, the subtests can be related to Horn and Cattell's fluid and crystallized intelligence, to Jenson's associative and cognitive levels, to Das's simultaneous and successive processes, and to Wechsler's verbal and performance scales.
The following subtests are contained in the DTLA-4: Word Opposites, Design Sequences, Sentence Imitation, Reversed Letters, Story Cons-truction, Design Reproduction, Basic Information, Symbolic Relations, Word Sequences, and Story Sequences.
DTLA-4 Software Scoring and Report System
This computerised program can be run on IBM-compatible PCs with Windows. Raw scores are converted into standard scores, percentile ranks, and age equivalents. The program calculates significant intra-ability differences.
What's new in the DTLA-4?
· Characteristics of the normative sample relative to socioeconomic factors, gender, disability, and other critical variables are the same as those reported in Statistical Abstract of the United States (U.S. Bureau of the Census, 1996) and are representative of the current U.S. population.
· The normative information is stratified by age relative to geography, gender, race, residence, ethnicity, and family income.
· Studies showing the absence of gender and racial bias have been added.
· Reliability coefficients are computed for subgroups of the normative sample (e.g., individuals with disabilities, females, Hispanics, African Americans) as well as for the entire normative sample.
Many new validity studies have been conducted; special attention has been devoted to showing that the test is valid for a wide variety of subgroups (including ethnic, racial, disability, and linguistic) as well as for a general population.
· All pictures in Picture Book 2 have been redrawn in colour to present a more appealing look to examinees.
· Each item on the test was re-evaluated using both conventional item analysis to choose "good" statistical items and the new differential item functioning analysis to find and eliminate biased items.
· The "Examiner Competence" section now explains more clearly who should and who should not administer the DTLA-4 and interpret its results.
· The number of cases in the test-retest study was increased considerably and coefficients were reported by age intervals. This enhances the confidence that one can have in the test's results.
· In addition to performing a principal components factor analysis on the subtests, the validity of the contrasting components was studied by employing a confirmatory factor analysis method.
· Because most authorities maintain that timed tests inherently bias against many people with disabilities, the administration procedures for the Story Sequences subtest have been redesigned to eliminate the time factor that existed in the DTLA-3 version of the subtest.
· To shorten the test, the Picture Fragments subtest was dropped. Of all the DTLA-3 subtests, this one was the least reliable and contributed little to understanding the constructs underlying the composites.
Complete DTLA-4 Kit includes Examiner's Manual; Picture Book 1 for Design Sequences, Design Reproduction, and Symbolic Relations; Picture Book 2 for Story Sequences and Story Construction; 25 Profile/Summary Forms; 25 Examiner Record Booklets; 25 Response Forms; Story Sequence Chips, and Design Sequence Cubes, all in a sturdy storage box. (1998)