What are the measurement properties of IQ scores and why do they matter? I hear terms like reliability, validity, standard error, and confidence intervals thrown around, but what do these actually mean for interpreting someone’s IQ score? How precise are these measurements really?
IQ scores aren’t perfectly precise measurements like height or weight. They have measurement error, meaning your “true” score falls within a range rather than being exactly the number reported. Understanding these properties prevents over-interpreting small score differences.
Key measurement properties include: (1) Reliability—how consistently the test measures (good IQ tests have reliability ~0.90-0.97); (2) Validity—whether it actually measures intelligence and predicts relevant outcomes; (3) Standard Error of Measurement (SEM)—typically 3-5 IQ points, meaning a score of 115 really means 110-120 with 68% confidence; (4) Test-retest stability—IQ is relatively stable but can fluctuate 5-10 points on retesting; (5) Flynn effect—scores increase ~3 points per decade, requiring regular test renorming. Understanding these properties prevents common mistakes like treating a 5-point difference as meaningful when it’s within measurement error, or assuming IQ scores are perfectly stable measures of fixed ability. Professional interpretation always considers confidence intervals and measurement precision, not just the point estimate.