FSIQ and the main WAIS indexes
FSIQ summarizes performance across the assessment. The index scores show the broad abilities that make up that overall level.
| Score | WAIS-IV | WAIS-5 | What it represents |
|---|---|---|---|
| FSIQ, Full Scale IQ | Yes | Yes | Overall intellectual ability across several kinds of task |
| VCI, Verbal Comprehension Index | Yes | Yes | Verbal knowledge, concept formation, and verbal reasoning |
| PRI, Perceptual Reasoning Index | Yes | No | Visual-spatial processing and fluid reasoning combined |
| VSI, Visual Spatial Index | No | Yes | Analyzing and constructing visual forms and spatial relationships |
| FRI, Fluid Reasoning Index | No | Yes | Finding rules and relationships in unfamiliar visual or quantitative problems |
| WMI, Working Memory Index | Yes | Yes | Holding information briefly while manipulating or updating it |
| PSI, Processing Speed Index | Yes | Yes | Fast, accurate visual search, matching, and output |
These composite scores use a scale with a mean of 100 and a standard deviation of 15.
FSIQ represents overall intellectual ability
FSIQ is the broadest summary of performance across the WAIS. It is calculated from designated subtest scaled scores, not by simply averaging the index scores. What FSIQ means explains its relationship with IQ, general intelligence, and the different WAIS-IV and WAIS-5 calculations.
VCI represents verbal knowledge, concepts, and reasoning
The Verbal Comprehension Index reflects the ability to use acquired vocabulary and general knowledge, identify conceptual relationships, and express an answer in words. Similarities and Vocabulary contribute in both editions; the wider subtest structure depends on the edition.
VCI is closely related to verbal comprehension and crystallized intelligence, but an index score remains a result from its particular WAIS tasks rather than a complete measure of every verbal ability.
PRI, VSI, and FRI separate two kinds of reasoning
In WAIS-IV, the Perceptual Reasoning Index combines two kinds of demand:
- visual-spatial processing, emphasized by tasks such as Block Design and Visual Puzzles; and
- fluid reasoning, emphasized by tasks such as Matrix Reasoning and Figure Weights.
WAIS-5 reports these separately. VSI uses Block Design and Visual Puzzles, while FRI uses Matrix Reasoning and Figure Weights. PRI is therefore not simply “nonverbal IQ,” and a WAIS-IV PRI score cannot be split mathematically into VSI and FRI. WAIS-IV and WAIS-5 compared explains why this separation matters.
The broader abilities are described in visuospatial processing and fluid reasoning.
WMI represents holding, manipulating, and updating information
The Working Memory Index reflects the ability to keep information active while reorganizing it or continuing a task. WAIS-IV WMI is built mainly from auditory tasks, including Digit Span and Arithmetic. WAIS-5 uses Digit Sequencing and Running Digits for its primary WMI and can also examine visual working memory through Symbol Span and Spatial Addition.
Working-memory performance depends on more than simple storage: attention, mental manipulation, updating, and the specific input format all matter. Working memory explains the broader ability.
PSI represents visual search, matching, and output speed
The Processing Speed Index reflects how quickly and accurately a person can scan simple visual information, compare it with a target or key, and respond under time limits. Symbol Search and Coding place different demands on visual search, decision speed, handwriting, and motor output.
PSI is not a single measure of how quickly someone understands a difficult idea, thinks in conversation, or solves every kind of problem. Processing speed explains the broader domain.
GAI and CPI regroup the profile
GAI, the General Ability Index, summarizes performance centered on knowledge and reasoning. CPI, the Cognitive Proficiency Index, summarizes working-memory and processing-speed performance. Both exist in WAIS-IV and WAIS-5, but their component subtests differ between editions.
GAI and CPI differences explains their construction and what a gap between them means.
Index levels and within-person differences both matter
An index score answers two separate questions: where the person stands compared with the same-age normative group, and where that domain sits within the person's own profile. A person's lowest index can still be above average, or their highest index can still be below average.
The practical meaning comes from combining those two comparisons with subtest demands and behavior during the assessment. How to read WAIS results develops that interpretation.