Intelligence & IQ Testing Summary

The Stanford-Binet test, established in 1916, is still widely utilized today.
- It is a modified and translated version of the original Binet-Simon test, which involved assessing cognitive abilities.
- A fundamental component of this test is comparing an individual's performance against established population norms.
- Baseline scores obtained from the general population allow comparisons of an individual's score to the average score of peers in the same age group.
The concept of the Intelligence Quotient (IQ) emerged concurrently with this testing, presenting a standardized measure of reasoning, problem-solving, and learning abilities relative to peers of the same age.
- IQ is calculated as follows:
  (IQ = (Mental ext{ } Age / Chronological ext{ } Age) \times 100)
- Mental age is defined by the score achieved on cognitive tests relative to the average performance of various age groups.
- Example:
- If a 6-year-old child achieves a score typical of an 8-year-old on a verbal reasoning test, their mental age is 8 despite their chronological age being 6.

A critical limitation of the IQ metric is its effectiveness, which diminishes with age.
- Intelligence tends to peak around 16 years but stabilizes thereafter, causing a discrepancy where IQ scores may decline as chronological age increases.
- This situation leads to lower calculated IQ scores for older adults, despite constancy in cognitive functioning.
Modern IQ tests have addressed this limitation by utilizing a deviation IQ model—especially pertinent for adults.
- Defining an average IQ at 100, this model assesses how far an individual's score deviates from this average, providing a more accurate representation of cognitive ability.
- For example, an IQ of 120 is indicative of above-average ability, while 80 indicates below-average ability.

Culture-Fair IQ tests focus on abstract reasoning skills that reduce linguistic and cultural biases, thereby creating a fair assessment environment.
- An example of a Culture-Fair IQ test is Raven's Progressive Matrices, which emphasizes non-verbal reasoning.

In adults, IQ scores remain relatively stable, with high test-retest reliability observed in WAIS scores (correlation of approximately 0.95 when retested after several weeks).
In children, especially under the age of two or three, IQ scores exhibit significant variability and instability.
- Early IQ measurements, particularly in the first six months, correlate poorly with adult IQ.
- Remarkably low IQ scores (e.g., below 50) in early childhood often predict subsequent disabilities.
- Research efforts have attempted to correlate infant IQ with cognitive measurements based on speed of habituation and response to novel stimuli:
- Infants who habituate to visual stimuli, such as a red circle, more rapidly tend to demonstrate higher IQs in later developmental phases.
- Infants showing more interest in new objects alongside familiar ones (e.g., previously shown faces) also correlate with higher later IQ scores.

Most modern IQ tests exhibit a moderate to high degree of correlation with one another.
IQ scores serve as moderate predictors of future academic achievement but do not guarantee success.
- Academic performance is influenced by a multitude of factors, including motivation, curiosity, diligence, and mental stamina.
Beyond academic success, IQ scores predicted performance across various professions and can be associated with health-related outcomes, such as health literacy.

IQ scores in the general population typically follow a bell curve distribution pattern.
- Most scores congregate around the mean, while fewer scores are found at the extremes.
The distribution encompasses two notable extremes:
1. Intellectual Disability:
- Characterized by a low IQ (under 70) and onset prior to adulthood, significantly impairing daily functioning.
- Four severity categories exist: mild (majority), moderate, severe, and profound.
  - Severe intellectual disabilities often arise from unique genetic mutations or birth-related accidents rather than family genetics.
- Notably common causes include Fragile X syndrome (mutation on the X chromosome) and Down syndrome (presence of an extra chromosome 21).
1. Mental Giftedness:
- Pertains to the top 2% of IQ scores; a large proportion of gifted individuals occupy influential professional roles (doctors, lawyers, engineers, professors).
- Lewis Terman’s longitudinal study of intelligent junior high schoolers illustrated that gifted individuals are not predisposed to "burn out" or mental illness.
  - Important takeaway: While genetic factors play a role in intelligence, practice and dedication are indispensable in realizing one's intellectual potential.