Measuring Intelligence

• Ratio IQ Calculation: Historically, IQ was calculated using the formula $IQ = \frac{MA}{CA} \times 100$, where $MA$ is mental age and $CA$ is chronological age.

• Individual Scales: Tests like the Wechsler Adult Intelligence Scale (WAIS) provide a composite score derived from multiple subtests measuring verbal and performance-based skills.

• Group Testing: Designed for mass administration, these tests are efficient but may lack the nuanced clinical observation possible in one-on-one settings.

• Culture-Fair Testing: These methods attempt to minimize linguistic and cultural bias by using non-verbal, abstract reasoning tasks like matrix patterns.

Reliability vs. Validity

• Reliability refers to the consistency of a test; a reliable test yields similar results upon retesting or when different versions are used.

• Validity refers to the accuracy of a test; a valid test actually measures the specific construct (intelligence) it claims to measure.

• Check the SD: When interpreting scores, always verify the standard deviation used (usually $15$), as a score of $130$ means something different if the SD were $10$.

• Distinguish Percentiles: Remember that an IQ score is not a percentage; a score of $100$ is the $50^{th}$ percentile, not $100\%$.

• Identify Bias: In exam scenarios involving lower-than-expected scores for specific groups, look for factors like 'Stereotype Threat' or linguistic barriers rather than innate ability.

• Verify Reliability: If a student takes two different versions of the same test and gets wildly different scores, the test lacks alternate-form reliability.

• The Reification Fallacy: Treating 'Intelligence' as a physical, tangible thing in the brain rather than an abstract statistical construct.

• Fixed Trait Myth: Assuming IQ is entirely genetic and unchangeable; in reality, environmental factors and the Flynn Effect (rising average scores over generations) show scores can shift.

• Predictive Limits: Overestimating what IQ predicts; while it correlates with academic success, it does not account for 'soft skills' like emotional intelligence or persistence.