# Foundations of Intelligence

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

## Measuring the Mind

**Francis Galton** made the first scientific attempt to measure intelligence in the late 19th century. He hypothesized that intelligence stemmed from sensory discrimination and reaction time, but these measures correlated poorly with real mental ability and were abandoned.

**Alfred Binet** and **Théodore Simon** created the first practical intelligence test in 1905 to identify French schoolchildren needing academic support. Binet introduced **mental age**, an age-equivalent score comparing performance to the typical average.

| Figure | Contribution | Outcome |
| --- | --- | --- |
| Galton | Sensory discrimination | Unsuccessful |
| Binet & Simon | First practical test | Introduced mental age |
| Terman | Stanford-Binet | Introduced ratio IQ |

**Common pitfall:** Assuming Binet's test was designed to rank children. It was strictly created to identify students needing extra academic support.

## The Ratio IQ Formula

**Lewis Terman** adapted Binet's test at Stanford, producing the **Stanford-Binet** test and the **intelligence quotient (IQ)** ratio:

$$IQ = \frac{\text{Mental age}}{\text{Chronological age}} \times 100$$

In this formula, **Mental age** is the tested performance level, and **Chronological age** is the actual physical age. For example, a 10-year-old with a mental age of 12 scores $12/10 \times 100 = 120$.

This ratio IQ formula worked well for children, but it broke down for adults because mental age growth eventually plateaus while chronological age keeps climbing. Modern tests solved this limitation with deviation IQ scores.

## Practice questions

5 of this lesson's 10 practice questions, with answers. The full set is in the app.

### 1. Order these figures by their historical contribution to measuring intelligence.

**Answer:**

1. Galton measures reaction time and sensory acuity, believing them to index intellect
2. Binet and Simon build a test to find schoolchildren needing extra help
3. Wechsler abandons the ratio, scoring each person against their own age group

**Why:** Galton's sensory approach came first and failed, Binet and Simon then built the first practical test with mental age, and Terman turned it into the Stanford-Binet with the ratio IQ. Each step built on the previous one's concept.

Page: https://tryals.app/practice/psychology-i/foundations-of-intelligence/order-these-figures-by-their-historical-contribution-to-measuring

### 2. Binet built his test to identify children needing **extra help**, and warned against treating the score as a fixed capacity. Within twenty years it was being used for exactly that. What does the history illustrate?

A. That the misuse was a misunderstanding later corrected by better statistics
B. That intelligence testing is inherently unethical and should not have been developed
C. That a measure's purpose is not carried in the number
D. That Binet's test was technically flawed, which invited misuse

**Answer:** C. That a measure's purpose is not carried in the number

**Why:** A score is portable and its purpose is not. Binet's diagnostic tool became a sorting instrument for immigration restriction and sterilisation laws, against his explicit warning, which is why 'what will this measure be used for by someone who does not share my aims' is a design question, not an afterthought.

Page: https://tryals.app/practice/psychology-i/foundations-of-intelligence/binet-built-his-test-to-identify-children-needing-extra-help-and

### 3. Select every statement that is TRUE about the foundations of intelligence testing.

A. Terman's ratio IQ formula worked reasonably well for children.
B. Binet introduced the concept of mental age.
C. How quickly you can react to a beep turned out to say almost nothing about how well you think.
D. The ratio formula broke down for adults.
E. Binet's test was built to rank children from smartest to least smart.

**Answer:** A. Terman's ratio IQ formula worked reasonably well for children.; B. Binet introduced the concept of mental age.; C. How quickly you can react to a beep turned out to say almost nothing about how well you think.; D. The ratio formula broke down for adults.

**Why:** Galton's poor correlations, Binet's mental age, the ratio formula's success for children, and its breakdown for adults are all true. Binet's test was practical (identifying support needs), not a smartest-to-least ranking - the one false option.

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

### 4. The ratio formula IQ = (mental age / chronological age) x 100 works reasonably for children and breaks down entirely for adults. Why does the arithmetic fail at the top of the age range?

A. Because mental age cannot be measured at all after adolescence, leaving the numerator undefined.
B. Because the multiplication by 100 becomes inappropriate once the ratio falls below 1.
C. Because mental age plateaus while chronological age keeps rising.
D. Because adults answer test items less carefully than children, so their mental age is underestimated.

**Answer:** C. Because mental age plateaus while chronological age keeps rising.

**Why:** The formula assumes both quantities keep climbing together, which stops holding once development levels off in the late teens, so the ratio falls for every adult alive and reports an unchanged 60-year-old at about 30. Wechsler abandoned the ratio: deviation IQ asks where you stand in your own age group, which is why modern scores still mean something at 60.

Page: https://tryals.app/practice/psychology-i/foundations-of-intelligence/the-ratio-formula-iq-mental-age-chronological-age-x-100-works

### 5. Binet and Simon's original 1905 test was created mainly to identify schoolchildren who needed extra academic support, not to produce a general ranking of intelligence.

**Answer:** True

**Why:** True. The test was commissioned by the French government to identify students needing additional support - an explicitly practical, applied purpose. Assuming it was built to rank children by intelligence is the named pitfall of this lesson.

Page: https://tryals.app/practice/psychology-i/foundations-of-intelligence/binet-and-simons-original-1905-test-was-created-mainly-to-identify