Understanding IQ: History, Measurement, and Predictive Power

Popular Culture and Personal IQ

IQ is a common term in popular culture.
Many people have varying beliefs about their own IQ scores.
The speaker has never taken an official IQ test and considers their intelligence to be slightly above average.
Skepticism exists regarding the accuracy of online IQ tests; however, practice tests are seen as helpful.

1904: Charles Spearman studies correlations between students' grades in subjects like English and Math.
- Identifies three possibilities: negative correlation, no correlation, or positive correlation.
- Spearman finds a clear positive correlation (0.64) among subjects, leading to his theory of the g-factor (general intelligence).
Alfred Binet and Theodore Simon develop the Binet-Simon test to identify students needing extra help in school, establishing the first IQ test.
- The IQ is derived by dividing mental age by chronological age and multiplying by 100.

The Binet-Simon test was translated and standardized by Lewis Terman to create the Stanford-Binet test.
Many other tests developed to measure the g-factor by assessing various mental abilities (memory, verbal, spatial, numerical).
Standardization of IQ scores (mean = 100, SD = 15).

Higher IQ tends to correlate with larger brain size (0.33).
Education: High IQ predicts school success and completion rates.
- Example: A study showed a correlation of 0.8 between 11-year-olds' IQ and their later GCSE performance.
Job Success: IQ is predictive, especially in complex jobs, with correlations ranging from 0.2 to 0.6.
- U.S. military sets IQ thresholds for recruits.
Longevity: Higher IQ may correlate with longer life; a Scottish study showed a 15-point IQ increase correlates with a 27% higher chance of survival to age 76.
Income: Moderate correlation (0.3) suggests higher IQ can lead to higher income, but many exceptions exist.

The eugenics movement in the U.S. used IQ for discriminatory practices, leading to forced sterilizations.
Early researchers believed intelligence was inherited and unchangeable, contributing to harmful ideologies.

Today's understanding suggests that IQ is influenced by both genetics and environment (50/50).
There are different types of intelligence: fluid (problem-solving) and crystallized (knowledge accumulation).
The Flynn Effect: Average IQ scores have increased over the past century; causes may include better nutrition, education, and changes in job types.

IQ tests often reflect cultural knowledge, potentially disadvantaging certain groups.
The concept of culture-fair tests is debated; complete cultural neutrality in tests is deemed impossible.
Motivation and test-taking strategies significantly impact IQ scores.

The speaker prepared for the IQ test by practicing various question types.
Test results showed strengths in quantitative reasoning but varied scores across different intelligence indices.

IQ tests are a controversial tool; they have predictive power but are often misunderstood.
Instead of defining worth, IQ should be viewed as one of many factors influencing outcomes in life.
Personal development and knowledge-building are crucial for success, transcending beyond IQ.