The Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV), is a widely used test designed to measure cognitive ability in adults and older adolescents, typically ranging from ages 16 to 90. Developed by psychologist David Wechsler, the WAIS-IV is an update to previous versions and continues to be one of the most respected tools in psychological assessment.

The WAIS-IV consists of 10 core subtests and 5 supplemental subtests that cover a range of cognitive functions, including verbal comprehension, perceptual reasoning, working memory, and processing speed. These subtests are grouped into four index scores:

1. Verbal Comprehension Index (VCI): Assesses verbal reasoning, concept formation, and the ability to understand and express ideas using words. Subtests include Vocabulary, Similarities, and Information.

2. Perceptual Reasoning Index (PRI): Measures non-verbal and fluid reasoning, spatial processing, and visual-motor integration. Subtests include Block Design, Matrix Reasoning, and Visual Puzzles.

3. Working Memory Index (WMI): Evaluates the ability to maintain and manipulate information in the mind over short periods. Subtests include Digit Span and Arithmetic.

4. Processing Speed Index (PSI): Assesses the speed and accuracy of visual identification, decision-making, and implementation. Subtests include Symbol Search and Coding.

The WAIS-IV also provides a Full-Scale IQ (FSIQ) score, which is derived from the four index scores and serves as a measure of overall intellectual ability. Additionally, the test can generate other composite scores, such as the General Ability Index (GAI) and Cognitive Proficiency Index (CPI), depending on the clinician's needs.

The test is typically administered individually by a trained psychologist and takes about 60 to 120 minutes to complete. The results are used in various contexts, including clinical diagnosis, educational planning, neuropsychological evaluation, and research. The WAIS-IV is praised for its reliability and validity, making it a key tool in assessing cognitive strengths and weaknesses in adults.