Question
Can IQ scores have decimals?
Short answer
In principle yes, but they are almost always reported as whole numbers. The IQ scale is continuous, so 117.4 is a meaningful point on it. In practice every score carries an error of several points, often about plus or minus 5 at 95% confidence, so a decimal would suggest a precision no test has.
Want your own number? The test is 25 visual puzzles, about 12 minutes, no sign-up.
The scale itself is continuous
A modern IQ is a standard score: your performance is placed on a scale where the mean of your age group is 100 and one standard deviation is 15 points (Wikipedia: Intelligence quotient). Nothing about that scale forces whole numbers. A person exactly 1.16 standard deviations above the mean sits at 117.4. Behind the scenes, scoring models such as the one IQ Octopus uses estimate ability on a continuous scale too.
Why reports round
The deciding factor is measurement error. Clinical full-scale IQ scores carry a standard error of a few points, and manuals report a confidence interval, often around plus or minus 5 points at 95% (Wechsler, 2008). If the honest answer is somewhere between 112 and 122, printing 117.4 would claim a precision the test cannot deliver. Rounding to 117 is already generous. That is also why good reports print a range next to the number.
Try one · Spatial Reasoning
Which option is the same shape, only rotated?
Tap the option you think is right, or show the answer.
Show the answer
Option 3 is the original figure turned a quarter turn clockwise.
How to solve it
- Pick a landmark: the marked cell or the end of the longest arm.
- Turn the figure in your head and watch where that landmark goes, and which side the other cells end up on.
- Turning the figure a quarter turn clockwise gives option 3.
- Each of the other options is a mirror image: flipping it over would match, but no turn does.
That was 1 puzzle. The full test has 25.
Where decimals do matter: percentiles
Percentiles bunch up at the ends of the curve. 140 is higher than about 99.62% of people and 145 than about 99.87%. Without decimals both would read as 100%, which is impossible. Our IQ score chart shows extra decimals in the tails for this reason. Try any score in the IQ percentile calculator.
How to read your number
- Treat the score as the middle of a range, not a precise value.
- Differences of a few points between two tests, or two attempts, are usually noise.
- The label band (for example High Average, 110 to 119) is a rough neighborhood; see the guide to reading an IQ score and how accurate an IQ score is.
Sources
- Intelligence quotient. Wikipedia. en.wikipedia.org/wiki/Intelligence_quotient
- Wechsler, D. (2008). WAIS-IV Technical and Interpretive Manual. Pearson.