The discontinue rule must be applied with care during administration and it is dependent on the assumption that subtest items proceed in order of difficulty. The discontinue rule assumes that having reached this point, individuals will fail to complete the remaining scale items due to the increased difficulty of items relative to their ability. The administration of WAIS-IV subtests relies on the discontinue rule, which aims to minimize testing time and differs for each subtest, with the examiner usually stopping the administration when the examinee obtains a score of 0 on a specified number of consecutive items. The WAIS-IV manual explains how to use start points, reversal rules, basal rules, and discontinue rules to calculate the total raw scores and convert them into scaled scores, under the assumption that the scale items are ordered according to their difficulty. There are also five supplemental subtests that can be used as an alternative to the core subtests in order to overcome problems such as a sudden illness or any other reason which might otherwise prevent fulfillment of the administration terms for instance, some individuals might have problems in motor skills that leave them unable to complete the Block Design subtest, which would thus be replaced by a supplemental subtest that does not require motor skills. It comprises 10 core subtests that yield four factor index scores (i.e., Verbal Comprehension, Perceptual Reasoning, Working Memory, and Processing Speed) as well as the full-scale IQ. The latest version of the WAIS, the fourth edition, introduced several improvements over previous editions : (1) Reduced administration time (2) updated structure to ensure compatibility with Carroll, Cattell, and Horn’s theoretical conceptualization of intelligence (3) addition of 53% new items (4) improved clinical utility and (5) revision of the subtests administered, the order of the items, a number of sample items, start-point items, stopping rule, the administration time, and bonus-point allotment. The Wechsler Adult Intelligence Scale (WAIS) is one of the most important measures developed to assess the cognitive abilities, and it has become an essential tool for a wide range of practitioners. Conclusions: Overall, the results suggest that the Egyptian WAIS-IV offers a highly valid assessment of intellectual abilities, despite the need for some improvements. Furthermore, most subtests have items that do not follow the difficulty rank they are ascribed in the WAIS-IV manual. However, each subtest included at least some items with limited ability to distinguish between individuals with differing levels of the cognitive variable being measured. Most items of the Egyptian WAIS-IV showed high discrimination, and the scale was adequately informative across the levels of latent traits (i.e., cognitive variables). Among IRT models, the two-parameter logistic model provided a good fit for dichotomous subtests, while the graded response model fitted the polytomous data. Results: Factor analysis indicated the unidimensionality of each subtest. In addition, factor analysis was performed to investigate the dimensionality of each subtest. The item-level and subtest statistical properties of the Egyptian WAIS-IV were established using a combination of four dichotomous IRT models and four polytomous IRT models. Methods: The sample consisted of 250 adults from Egypt. This study investigates item and scale properties of the Egyptian WAIS-IV using item response theory (IRT) models. Background: The Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) has been adapted to 28 different cultures and there has been considerable interest in examining its structure through exploratory and confirmatory factor analysis.
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