Source: PSYCH 1100 General Psychology, The Ohio State University | Guided Notes, Pages 392–405
Difficulty: Introductory | Prerequisites: None. This is foundational material for the intelligence unit.
Intelligence is the capacity to understand complex ideas, adapt to the environment, learn from experience, and reason through problems. Psychologists measure it using standardised tests (Stanford-Binet, Wechsler) that compare your score to a normal distribution of same-age peers. There is ongoing debate about whether intelligence is one general ability ("g") or many separate ones, including emotional intelligence.
Intelligence
The ability to understand complex ideas, adapt effectively to the environment, learn from experience, engage in reasoning, and overcome obstacles.
In simple terms, it is the broad capacity to figure things out, learn, and cope with new situations.
Mental age
A score on Binet and Simon's early test representing the age level at which a child is performing intellectually, regardless of their actual (chronological) age.
Think of it as: if a 6-year-old solves problems that most 8-year-olds solve, that child has a mental age of 8.
Intelligence Quotient (IQ)
Originally proposed by Lewis Terman (1916) as a ratio: (mental age / chronological age) x 100. Modern IQ is no longer calculated this way; it is based on where your score falls on a normal distribution compared to same-age peers.
In simple terms, IQ is a standardised score showing how your cognitive ability compares to others your age, with 100 as the average.
General intelligence (g)
Spearman's concept of a single, broad mental capacity that underlies performance across all cognitive tasks. People who do well on one type of mental test tend to do well on others.
Think of it as: g is the "common engine" powering all your different mental abilities.
Specific abilities (s)
Narrow, domain-specific skills (e.g. musical ability, spatial reasoning) that exist alongside g in Spearman's two-factor theory.
Fluid intelligence (Gf)
The ability to think logically and solve novel problems without relying on previously learned knowledge. Examples include pattern recognition, abstract reasoning, and creative problem-solving.
In simple terms, fluid intelligence is your raw reasoning power when you face something you have never seen before.
Crystallised intelligence (Gc)
The ability to use knowledge, skills, and experience you have already acquired. Examples include vocabulary tests and general knowledge quizzes.
Think of it as: everything you have learned and stored that you can draw on when needed.
Emotional intelligence (EQ)
The capacity for self-awareness, self-management, motivation, empathy, and social skills. EQ may predict success in relationships and workplace outcomes better than traditional IQ.
Normal distribution (bell curve)
The symmetrical, bell-shaped curve that IQ scores follow in large populations. The mean is set at 100, and about 68% of scores fall within 15 points of the mean (between 85 and 115).
Flynn Effect
The well-documented worldwide rise in IQ scores of roughly 3 points per decade over the past century. Likely driven by environmental improvements such as better nutrition, education, and reduced exposure to toxins.
Heritability (of intelligence)
The proportion of variation in IQ within a population attributable to genetic differences. For intelligence, heritability is approximately 0.75, meaning about 75% of the variation between individuals in a given population is linked to genetics.
In simple terms, genes explain most of the differences in IQ between people, but environment still matters, especially at the extremes.
Psychologists define intelligence as a cluster of abilities rather than one single trait. The core components are:
Understanding complex ideas
Adapting effectively to the environment
Learning from experience
Engaging in reasoning
Overcoming obstacles
This definition is deliberately broad. Intelligence is not just "book smarts" or test scores; it captures how flexibly and effectively a person can navigate new problems and environments.
Binet and Simon (1904)
Alfred Binet and Theodore Simon developed the first practical intelligence test in France. Their key assumptions and contributions:
More intelligent children perform cognitively like older children
They introduced the concept of "mental age," the intellectual level at which a child is functioning
Their goal was practical: predict which children would struggle in school so they could receive extra support
Lewis Terman and the IQ score (1916)
Terman, a Stanford psychologist, adapted Binet's test for American use and introduced the Intelligence Quotient:
Ratio IQ formula: (mental age / chronological age) x 100
Example: a 10-year-old performing at a 12-year-old level has an IQ of (12/10) x 100 = 120
The fatal flaw of ratio IQ: because mental age plateaus in adulthood while chronological age keeps rising, the formula makes adults appear to lose intelligence as they age. This is a mathematical artefact, not a real cognitive decline.
Today, psychologists use deviation IQ, not ratio IQ. The two major test families are:
Stanford-Binet Intelligence Scales (descended from the original Binet-Simon test)
Wechsler Intelligence Scales (separate versions for adults, children, and preschoolers)
How modern IQ scoring works:
Hundreds of people in each age group take the test to establish a normal distribution of scores
An individual's raw score is then placed on that distribution for their age group
The result tells you where you fall relative to your peers, not your absolute mental age
The mean is set at 100, with a standard deviation of 15
About 68% of people score between 85 and 115 (within one standard deviation of the mean)
About 95% score between 70 and 130 (within two standard deviations)
Less than 2% score above 130 or below 70
Charles Spearman studied school-aged children's performance across various cognitive tasks and noticed a consistent pattern: children who did well on one type of task tended to do well on others.
From this he proposed two factors:
General intelligence (g): a broad mental capacity that influences performance on all cognitive tests. This includes verbal, mathematical, spatial, and logical skills.
Specific abilities (s): narrow, domain-specific skills that apply to particular tasks.
Spearman focused primarily on g, and most major intelligence tests (Stanford-Binet, Wechsler) were designed to measure g rather than s.
Cattell and Horn later divided g into two components:
Fluid intelligence (Gf): reasoning and problem-solving with novel material, independent of prior learning. Examples: pattern recognition, abstract puzzles, creative thinking.
Crystallised intelligence (Gc): applying knowledge and skills already acquired through education and experience. Examples: vocabulary, general knowledge, reading comprehension.
How they change over the lifespan:
Fluid intelligence peaks in young adulthood and gradually declines with age
Crystallised intelligence continues to grow throughout life, as you accumulate knowledge and experience
This is why older adults may struggle with speeded novel tasks but remain strong (or improve) on knowledge-based ones
Some researchers argue Spearman underestimated specific abilities. The core claim is that there may be multiple independent types of intelligence, with no single "g" dominating them all.
EQ is one of the most discussed alternatives to traditional IQ. Its five components:
Self-awareness
Self-management
Motivation
Empathy
Social skills
Key findings about EQ:
EQ may be a better predictor of workplace success, relationship quality, and life satisfaction than IQ
EQ and IQ appear to be separable. Some conditions illustrate this: individuals with Autism Spectrum Disorder (ASD) may have high IQ but lower EQ, while individuals with Down syndrome may show the reverse pattern.
EQ influences academic and professional outcomes beyond what IQ predicts
A classic study illustrating the power of self-regulation (an EQ-related skill):
Children were given one marshmallow and told they could have a second if they waited for the experimenter to return
Some children waited; others did not
When researchers followed up 12 years later, the children who had delayed gratification showed better career performance and higher life satisfaction
This study is often cited to show that self-regulation and emotional control matter for long-term outcomes, independently of IQ.
Students often think IQ is still calculated as a ratio (mental age / chronological age x 100). It is not. Modern IQ uses deviation scoring based on the normal distribution.
Students confuse fluid and crystallised intelligence. Fluid is about novel problem-solving without prior knowledge; crystallised is about applying what you already know. A vocabulary test measures crystallised intelligence, not fluid.
Students sometimes assume "g" means there is only one type of intelligence. Spearman acknowledged specific abilities (s) as well; he simply argued that g was the dominant factor.
Students often think EQ and IQ measure the same thing. They appear to be separable constructs. A person can score high on one and low on the other.
⚠️ Know the difference between ratio IQ and deviation IQ, and why ratio IQ was abandoned.
⚠️ Be able to distinguish fluid intelligence from crystallised intelligence, with examples of each.
⚠️ Understand what the normal distribution of IQ scores looks like: mean of 100, SD of 15, and the 68%/95% rules.
⚠️ Know the five components of emotional intelligence (EQ) and how EQ differs from IQ.
⚠️ Be prepared to explain Spearman's two-factor theory (g vs. s) and why most tests focus on g.
⚠️ The marshmallow test and delayed gratification are commonly tested as an example of EQ predicting real-world outcomes.
True or false: Modern IQ tests calculate your score by dividing mental age by chronological age.
Fill in the blank: About ___% of people score between 85 and 115 on the Wechsler scale.
True or false: Fluid intelligence tends to increase throughout the entire lifespan.
Fill in the blank: Spearman called broad, overall cognitive ability ____ and narrow domain-specific skills ____.
True or false: EQ and IQ always rise and fall together.
Answers: 1. False (modern tests use deviation IQ). 2. 68%. 3. False (it peaks in young adulthood then declines; crystallised intelligence is the one that keeps growing). 4. g; s. 5. False (they are separable).
Q: What was the main problem with Terman's ratio IQ formula?
A: Because mental age plateaus in adulthood while chronological age keeps increasing, the formula produces artificially declining IQ scores as people get older. This made it seem as though adults were losing intelligence, which is a mathematical artefact rather than a real change.
Q: How do modern intelligence tests determine an individual's IQ score?
A: They compare the individual's raw score to a normal distribution of scores from hundreds of same-age peers. The individual's position on that distribution determines their IQ, with 100 as the mean and a standard deviation of 15.
Q: Explain the difference between fluid intelligence and crystallised intelligence, and give one example of each.
A: Fluid intelligence is the ability to reason and solve novel problems without relying on prior knowledge (e.g. solving a new type of logic puzzle). Crystallised intelligence is the ability to apply previously acquired knowledge and skills (e.g. a vocabulary or general knowledge test).
Q: According to Spearman's two-factor theory, why do people who score well on one cognitive test tend to score well on others?
A: Spearman attributed this to general intelligence (g), a broad mental capacity that underlies performance across all types of cognitive tasks. While specific abilities (s) exist for particular domains, g is the common factor driving the positive correlations between different tests.
Q: Name three components of emotional intelligence (EQ) and explain why EQ matters beyond IQ.
A: Three components of EQ are self-awareness, empathy, and self-management. EQ matters because it may be a better predictor of workplace relationships, romantic relationships, and overall life satisfaction than traditional IQ. The marshmallow study showed that children who could delay gratification (an aspect of self-regulation related to EQ) had better career outcomes 12 years later.
This material connects directly to the biological bases of behaviour (Chapter 3), since brain structure and function (prefrontal cortex, cortical thickness) correlate with IQ. The genetics discussion ties into the nature vs. nurture debate covered in the development chapter.
Emotional intelligence links to social psychology and motivation topics later in the course. The concept of delayed gratification also appears in discussions of operant conditioning and self-regulation.
The normal distribution and standard deviation concepts here are the same statistical tools used throughout research methods in psychology.
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