The Differential Ability Scales (DAS) was developed by Collin. D. Elliott. The main idea was to differentiate between people on the basis of their different levels of abilities. He included ‘g’ factor in development of DAS but mainly focused upon individual intellectual strengths and weaknesses.
But it was not a new development. In fact he expounded upon the already developed British Ability Scales and shared the latest versions of the Stanford-Binet and Wechsler scales.
However, the manual of the Differential Scales, "Introductory and Technical Handbook", claims that it is different from other intelligence tests on a number of accounts:
• The term ‘intelligence’ and the ‘IQ’ are not part of the DAS as it focuses mainly upon individual abilities.
• It is different from other psychological tests of the day for its administration, procedures and technical qualities.
• The organization, scoring and interpretation of the differential scales focus upon the well defined areas of the behaviors which are to be assessed.
While perusing the handbook, you will find 20 sub-tests included in the Differential Ability Scale. The manual claims that these sub-tests are included on theoretical as well as empirical rationale. The theoretical side is flexible. It uses hierarchical approach to mental abilities which can accommodate different levels. It also provides a broad base of information which can help the psychologists to derive certain hypothesis about the subjects.
The empirical side is a bit rigid but focuses upon your cognitive abilities. The Differential Ability Scale is built in a way that both theoretical and the empirical rationales coordinate to each other.
The DAS includes the following sub-tests divided into three categories:
• Block Building
• Verbal Comprehension
• Picture Similarities
• Naming Vocabulary
• Early Number Concepts
• Pattern Construction
• Recall of Designs
• Word Definitions
• Word Similarities
• Sequential and Quantitative Reasoning
Diagnostic Sub tests
• Matching Letter-Like Forms
• Recall of Digits
• Recall of Objects
• Recognition of Pictures
• Speed of Information Processing
• Basic Number Skills
• Word Reading
The normalization of any psychological test is the process which determines its technical strength. The Differential Ability Scales is different from others due to the fact that it encompasses research and normalization process of the British Ability Scale. The developer of the Differential Ability Scales took the work of two decades made upon the BAS. He analyzed the planning, construction and standardization procedures of the BAS to develop his own model.
Collin. D. Elliott developed standardization process of the Differential Ability Scales with a lot of care. He took a sample basing upon a big population of the non-institutionalized English proficient people of different ages with their ratio as mentioned by Bureau of the Census for the most recent period available at that time. He also observed other factors such as sex, race, ethnicity and geographical distributions.
The issue of reliability and validity of any psychological test has got more importance that it was originally considered. The testing industry has been focusing in developing test with a high level of reliability and validity while the opponents of the tests have been finding the loopholes in the reports. Reliability of tests may roughly be defined as the differences between the scores taken at different times upon the same subjects.
Collin. D. Elliott has claimed reliability of DAS from .79 to .94 which is solidly high in comparison to the other tests available in the field. The reliability of the sub-tests ranges from .38 to .94, with a majority standing at .60 to .90.
The DAS handbook represents some comparison between IRT-based (item response theory-based) and traditional internal consistency coefficients. In these cases, the reliability figures produced by both methods are found in close agreement.
The validity of the DAS has been explored internally and externally. The results from the both types of analysis are almost the similar. The handbook provides evidence that the abilities become more differentiated with increasing age. It contains a lot of data about external validity of the DAS. The major sources of such data are:
1- Correlation between the DAS scores and scores on other multiple batteries such as Stanford Binet and Wechsler scales.
2- Correlation between scoring of the cognitive subtests of the DAS and other batteries of the day such as Peabody Picture Vocabulary Test Revised (PPVT-R) and Woodcock Reading Mastery Tests-Revised (WRMT-R), and
3- Special attention on the special population such as gifted, learning disabled or mentally retarded people.
Aylward and Reinchr have rightly observed that complexity of the administration and scoring procedures of the Differential Ability Scales may obstruct its popular usage in the applied environment. Furthermore, he DAS is a comparatively new scale which needs a lot of research and feeding before it can prove its importance in the job market as well as in the clinical atmosphere.
Whatever the criticism it may attract, the Differential Ability Scales has established its place in the psychometrics. It is a powerful psychological instrument which can be used in any given situation and can produce such authentic results as any other psychometrics tool may do. It also provides flexibility which helps the psychologists to use it for the children as well for the adults to measure their different level of abilities.
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