This cheat sheet covers major ideas in intelligence and IQ testing, including how psychologists define intelligence, measure it, and interpret test scores. Students need this topic to understand what IQ tests can show and what they cannot prove. It also helps students evaluate claims about intelligence in school, research, and society.
The core ideas include general intelligence, multiple intelligences, emotional intelligence, standardization, reliability, validity, and cultural bias. A common historical formula is IQ = mental age / chronological age x 100, but modern IQ tests usually use standard scores. Most modern IQ tests have a mean of 100 and a standard deviation of 15.
Test results should be interpreted with context, because motivation, language, culture, health, and opportunity can affect performance.
Key Facts
- The historical IQ formula is IQ = mental age / chronological age x 100.
- Modern IQ tests usually use standard scores with a mean of 100 and a standard deviation of 15.
- A score of 115 is one standard deviation above the mean on many IQ tests because 100 + 15 = 115.
- Reliability means a test gives consistent results across time, versions, or scorers.
- Validity means a test measures what it claims to measure and supports accurate interpretations.
- Standardization means the test is given and scored the same way for everyone using a comparison group.
- A percentile rank shows the percentage of people in the norm group who scored at or below a given score.
- Cultural bias can occur when test content or testing conditions advantage one group over another for reasons unrelated to intelligence.
Vocabulary
- Intelligence
- Intelligence is the ability to learn from experience, solve problems, adapt to new situations, and use knowledge effectively.
- IQ
- IQ is a score used to summarize performance on certain standardized tests of cognitive ability.
- General intelligence
- General intelligence, or g, is the idea that one broad mental ability influences performance across many cognitive tasks.
- Standardization
- Standardization is the process of giving, scoring, and comparing a test in a consistent way using a norm group.
- Reliability
- Reliability is the degree to which a test produces stable and consistent results.
- Validity
- Validity is the degree to which evidence supports the intended use and interpretation of a test score.
Common Mistakes to Avoid
- Treating IQ as a complete measure of a person is wrong because IQ tests measure selected cognitive skills, not creativity, character, motivation, wisdom, or life potential.
- Confusing reliability with validity is wrong because a test can be consistent but still fail to measure the intended ability.
- Using the old IQ formula for all modern tests is wrong because most current IQ tests are based on standard scores, not mental age divided by chronological age.
- Ignoring the norm group is wrong because an IQ score only has meaning when compared with the population used to standardize the test.
- Assuming group score differences are purely genetic is wrong because environment, schooling, nutrition, stress, discrimination, language, and testing conditions can influence results.
Practice Questions
- 1 A 10-year-old child has a mental age of 12 on an older-style test. Using IQ = mental age / chronological age x 100, what is the IQ?
- 2 On a modern IQ test with mean 100 and standard deviation 15, how many standard deviations above the mean is a score of 130?
- 3 A student scores in the 84th percentile on a cognitive ability test. What does this percentile rank mean?
- 4 Why should psychologists consider culture, language, and testing conditions when interpreting IQ test scores?
Understanding Intelligence & IQ Testing
An intelligence test samples certain mental tasks during a limited time. These tasks may involve finding patterns, remembering information, defining words, solving visual puzzles, or working quickly with simple symbols. A person does not show every ability they have in one testing session.
The score is an estimate based on a sample of performance. Psychologists call the underlying ability being studied a construct.
Intelligence is a construct because it cannot be observed directly like height or weight. Test makers must decide which tasks give useful evidence about that construct.
Good measurement depends on more than giving everyone identical instructions. The comparison group, often called the norm group, must be large enough and varied enough to represent the population for which the test will be used. Test publishers update norms because school experiences, health, technology, and population patterns can change over time.
Scores can slowly rise or fall across generations even when the test questions stay similar. This means an older scoring system may not give a fair comparison for students today.
Every test score contains some measurement error. A student may earn a somewhat different result on another day because of sleep, illness, stress, distraction, practice, or random variation. For this reason, trained professionals often use a confidence range rather than treating one number as exact.
They look for patterns across several parts of a test. For example, a student might show strong verbal reasoning but lower processing speed. That pattern can guide further support, but it does not prove that the student is smart in only one way or incapable in another.
Validity requires evidence for the use being made of a score. A test that helps predict success in a certain type of schoolwork may still be a poor tool for judging creativity, kindness, practical skill, or future success in life. This matters in school decisions such as identifying a learning disability, planning accommodations, or considering advanced programs.
A careful evaluation uses classroom work, teacher observations, family information, achievement measures, and the student’s history. No single test should carry the full weight of an important decision.
Bias is not simply the fact that groups earn different average scores. Psychologists investigate whether items, language, examples, scoring, or testing conditions create an unfair barrier for particular groups. A vocabulary item may reflect access to certain experiences rather than reasoning ability.
Limited familiarity with the test language can affect performance even when a student understands the underlying idea. When studying this topic, separate the meaning of a score from claims about a person’s worth.
An IQ result describes performance under specific conditions compared with a particular norm group. It is useful evidence, but it is not a complete description of a human mind.