# Psychometric Theories of Intelligence

Psychology I · Individual Differences · https://tryals.app/learn/psychology-i/psychometric-theories-of-intelligence

## Spearman vs. Thurstone

Is intelligence one single capacity, or a collection of many? **Charles Spearman** used **factor analysis** to show that scores on diverse cognitive tests correlate, leading to his **two-factor theory**: a single **general intelligence factor (g)** drives all test performance, alongside narrow **test-specific factors (s)**.

**Louis Thurstone** challenged this, proposing **seven Primary Mental Abilities**—such as verbal comprehension, spatial visualization, and memory—as independent faculties. 

| Theorist | Core Structure | Primary Claim |
| --- | --- | --- |

| **Spearman** | Hierarchical | One core **g** factor plus task-specific **s** |
| **Thurstone** | Pluralistic | Seven distinct, independent mental abilities |

**Pitfall:** Later re-analyses proved Thurstone's seven abilities still correlate with each other above chance, meaning a broad general factor lurks even beneath his multiple abilities.

## Cattell's Fluid and Crystallized Intelligence

**Raymond Cattell** split general intelligence into two distinct components that age in opposite directions.

**Fluid intelligence (Gf)** is the capacity to reason and solve novel problems independently of learned knowledge. It peaks in early adulthood and declines with age.

**Crystallized intelligence (Gc)** is accumulated knowledge and vocabulary built through experience. It remains stable or increases well into later life.

| Intelligence Type | Core Definition | Trajectory with Age |
| --- | --- | --- |
| **Fluid (Gf)** | Novel problem-solving | Declines after early adulthood |
| **Crystallized (Gc)** | Accumulated knowledge | Stable or increases with age |

Modern models synthesize these views hierarchically: **g** sits at the top, broad abilities like **Gf** and **Gc** sit beneath it, and narrow skills form the base.

## Practice questions

7 of this lesson's 12 practice questions, with answers. The full set is in the app.

### 1. Order the psychometric theories by how much structure they claim intelligence has, from the simplest to the most elaborate.

**Answer:**

1. One general factor accounts for performance across every cognitive test
2. Two broad kinds: reasoning with novel material, and accumulated knowledge
3. Seven primary abilities, related but worth distinguishing
4. A hierarchy: one general factor above broad abilities above narrow ones

**Why:** Laid out this way the century-long argument looks less like a series of contradictions and more like a question of resolution. Spearman saw one thing; Cattell and Horn split it in two along a line that predicts different age trajectories; Thurstone distinguished seven.

The hierarchical model is last because it is not a rival to the others but an arrangement of them. Narrow abilities sit at the bottom, broad ones like fluid and crystallized in the middle, and g at the top - and each earlier theory turns out to have been describing one storey of the same building.

Which is also why the data never settled the original dispute by refuting anyone. Thurstone's seven abilities correlate, so a general factor can be extracted from them; Spearman's g does not preclude meaningful distinctions beneath it. Both men were reading a real structure at the level of detail their method encouraged.

Page: https://tryals.app/practice/psychology-i/psychometric-theories-of-intelligence/order-the-psychometric-theories-by-how-much-structure-they-claim

### 2. Fluid intelligence peaks in the twenties and declines from there; crystallized intelligence keeps rising into old age. Why does the distinction predict that an older adult can be worse at a novel puzzle and better at their job?

A. Because job performance does not depend on intelligence, so the decline in fluid ability is irrelevant to it.
B. Because crystallized intelligence replaces fluid intelligence with age, taking over the same functions.
C. Because the two draw on different resources.
D. Because older adults are more motivated at work than in laboratory tasks, so their scores differ by setting.

**Answer:** C. Because the two draw on different resources.

**Why:** The two abilities have different inputs, which is why they have different trajectories: fluid reasoning has no prior knowledge to draw on, and crystallized ability *is* the accumulated knowledge. An older engineer solving a problem in her field is deploying pattern recognition built over decades, put her in front of a puzzle designed to defeat prior knowledge and the support is removed.

Page: https://tryals.app/practice/psychology-i/psychometric-theories-of-intelligence/fluid-intelligence-peaks-in-the-twenties-and-declines-from-there

### 3. Because Thurstone's seven primary abilities correlated with one another, he concluded that Spearman's single g was correct after all.

**Answer:** False

**Why:** False. The correlations were the basis for a *second-order* factor, and the debate continued rather than resolving. Thurstone maintained the primary abilities were the useful level of description. Modern hierarchical models like Carroll's three-stratum theory keep both, with g at the top and specific abilities beneath.

Page: https://tryals.app/practice/psychology-i/psychometric-theories-of-intelligence/because-thurstones-seven-primary-abilities-correlated-with-one

### 4. Sort each ability-plus-age pattern by which intelligence it fits.

**Answer:**

- Fluid intelligence (Gf): Solving an abstract, unfamiliar reasoning puzzle - tends to decline with age, Quickly grasping the rule behind a brand-new pattern
- Crystallized intelligence (Gc): A large vocabulary that keeps growing into old age, Rich general knowledge accumulated over decades

**Why:** Novel, knowledge-independent reasoning that declines with age is fluid; accumulated vocabulary and knowledge that holds or rises is crystallized. The opposite aging trajectories are the sharpest way to tell them apart.

Page: https://tryals.app/practice/psychology-i/psychometric-theories-of-intelligence/sort-each-ability-plus-age-pattern-by-which-intelligence-it-fits

### 5. Select every statement that is TRUE about psychometric theories.

A. Thurstone's seven abilities still correlated more than chance would predict.
B. Fluid and crystallized intelligence age in the same direction.
C. Thurstone proposed seven primary mental abilities.
D. Modern models often arrange g and specific abilities hierarchically.
E. Spearman used factor analysis to argue for a general factor g.

**Answer:** A. Thurstone's seven abilities still correlated more than chance would predict.; C. Thurstone proposed seven primary mental abilities.; D. Modern models often arrange g and specific abilities hierarchically.; E. Spearman used factor analysis to argue for a general factor g.

**Why:** Spearman's g, Thurstone's seven abilities, their residual correlation, and the modern hierarchical synthesis are all true. Fluid and crystallized intelligence age in OPPOSITE directions - the one false option.

Page: https://tryals.app/practice/psychology-i/psychometric-theories-of-intelligence/select-every-statement-that-is-true-about-psychometric-theories

### 6. IQ scores are strikingly stable across decades, yet the Flynn effect shows raw performance rising fast between generations. How can both be true?

A. Because the Flynn effect applies only to some countries, leaving others stable
B. Because stability is about rank and the Flynn effect about absolute level
C. They cannot both be true; one of the two findings must be an artefact
D. Because IQ is renormalised each year, which erases individual change too

**Answer:** B. Because stability is about rank and the Flynn effect about absolute level

**Why:** Rank and level are different measurements. Your position among peers holds across decades while the entire distribution moves, so a person is stable and their cohort is not, and only the second is invisible in a score pinned to a mean of 100.

Page: https://tryals.app/practice/psychology-i/psychometric-theories-of-intelligence/iq-scores-are-strikingly-stable-across-decades-yet-the-flynn-effect

### 7. Spearman inferred a single general factor; Thurstone argued for seven relatively independent abilities. Both were analysing correlations among mental tests. How did they reach opposite conclusions from the same kind of data?

A. Because Thurstone's tests were simply unreliable.
B. Because factor analysis does not deliver one unique answer.
C. Because Spearman studied children and Thurstone adults.
D. Because Thurstone used a much larger sample.

**Answer:** B. Because factor analysis does not deliver one unique answer.

**Why:** Factor analysis extracts a structure and does not tell you which is correct, an unrotated solution produces a large first factor, and rotating for simple structure spreads the variance. The resolution came from Thurstone's own data: his seven abilities correlated with each other, and factoring those correlations produces something that looks a great deal like g.

Page: https://tryals.app/practice/psychology-i/psychometric-theories-of-intelligence/spearman-inferred-a-single-general-factor-thurstone-argued-for-seven