Wechsler Adult Intelligence Scale (WAIS)

The Wechsler Adult Intelligence Scale is an individually administered test of cognitive ability for people aged 16 to 90 years. It provides a full scale intelligence quotient (FSIQ) and index scores across several cognitive domains: verbal comprehension, perceptual reasoning, working memory and processing speed.

Scores are normed with a mean of 100 and an SD of 15. The test is administered by a trained clinical psychologist and takes about 60 to 90 minutes.

Usage. It is used to assess intellectual disability, specific cognitive strengths and weaknesses, the effects of brain injury, and educational and occupational needs.

Indications. Suspected intellectual disability, cognitive decline after head injury or neurological illness, assessment of specific learning difficulties, medicolegal capacity assessments, and planning of educational or occupational support.

Preparation and technique. The test is given in a quiet room with the patient rested. Subtests are administered in a fixed order, and the patient's effort and behaviour are recorded. Sensory aids such as glasses and hearing aids are used.

Contraindications and precautions. Acute illness, severe depression, psychosis, intoxication and poor effort reduce validity. Language barriers and sensory impairment need adapted assessment.

Interpretation.

• An FSIQ of 90 to 109 is in the average range.
• An FSIQ of 70 or under falls at about two SDs under the mean and is one element in the assessment of intellectual disability.
• Intellectual disability requires impairment in adaptive functioning, as well as a low score, and onset in the developmental period.
• Large differences between indices, or between verbal and perceptual scores, are clinically significant and suggest specific difficulties.

Causes of a low score. Intellectual disability, brain injury, dementia, severe mental illness, sensory impairment, language barrier, and poor effort.

Critical values and findings needing immediate action. A marked fall from a previous baseline in an adult requires prompt neurological and medical assessment for acute cause.

Limitations and artefacts. Practice effects limit retesting within a short interval. Scores are influenced by education, culture and language. The test does not measure all aspects of ability, including creativity and practical skills.

Follow up tests. Assessment of adaptive functioning, neuropsychological testing of memory and executive function, neuroimaging where a brain lesion is suspected, and genetic testing where intellectual disability is confirmed.

Special groups. Older adults are interpreted with age specific norms, and processing speed declines normally with age. People with sensory or motor impairment need adapted administration.