The Wechsler Adult Intelligence Scale - Fourth Edition (WAIS-IV) is the gold standard clinical instrument used globally to diagnose cognitive strengths, developmental gifts, or processing difficulties. Rather than yielding a single flat score, it breaks human intelligence into 4 core functional index scores.
1. The Four Index Indices of WAIS-IV
- Verbal Comprehension Index (VCI): Reflects language comprehension, abstract conceptual reasoning, and accumulated cultural knowledge (Crystallized).
- Perceptual Reasoning Index (PRI): Evaluates non-verbal spatial reasoning, visual integration, and novel rule-solving (Fluid).
- Working Memory Index (WMI): Evaluates the ability to hold verbal and numerical details in mind while actively manipulating them.
- Processing Speed Index (PSI): Measures the rate at which visual, abstract patterns can be scanned, sorted, and recorded.
2. FSIQ Scoring and Standard Deviation
The FSIQ (Full Scale IQ) is mathematically computed from 10 core subtests across the 4 indices. It uses a strict standard deviation scale (SD = 15, Mean = 100), meaning IQ 130 is 2 standard deviations above average, representing the 97.7th percentile.
