Reaction Time And IQ
There is a relationship — but it is weak, mediated, and tells you almost nothing about a single person.
TL;DR — Pooled studies show a correlation of roughly r = -0.2 to -0.3 between simple RT and IQ (faster RT, higher IQ). That is real at the group level and useless at the individual level.
A correlation of 0.25 means reaction time explains about 6% of the variance in IQ scores. The other 94% is something else.
The headline numbers
Sheppard & Vernon (2008) meta-analysed 172 studies covering 53,000 participants. Mean correlation between simple RT and IQ: -0.24. For choice RT: -0.31. Deary (2011) replicated this in the UK Biobank with a similar effect size.
Why the correlation exists at all
- Both traits load on a shared "processing speed" factor.
- Neural conduction velocity (axon myelination) affects both.
- Both decline with age along similar curves.
- Both are sensitive to sleep, glucose and arousal state.
Why you should not over-interpret it
An individual prediction at r = 0.25 has confidence intervals so wide that knowing a person's RT tells you almost nothing about their IQ — and vice versa. The relationship is real and useful for population-level neuroscience; it is meaningless as a personal verdict.
What changes the correlation
| Condition | Correlation magnitude |
|---|---|
| Simple visual RT vs full-scale IQ | ~0.24 |
| Choice RT (4-option) vs IQ | ~0.31 |
| Inspection time vs IQ | ~0.40 |
| RT variability vs IQ | ~0.35 |
Frequently Asked Questions
Does a fast reaction time mean I am smart?
Statistically a little — practically, no. The signal is too noisy at the individual level.
Why is RT variability a better predictor than mean RT?
Consistency of attention loads strongly on g (general intelligence), more than peak speed does.
Can I raise IQ by training reaction time?
No replicated evidence supports far transfer from RT training to IQ.
Test Your Reaction Time Now
Free. 90 seconds. Global leaderboard. No download.
Start Test