GUIDES FOR UNDERSTANDING
Average IQ: What a mean of 100 and 15-point spread mean
Many standardised intelligence tests place the centre of their reference scale at 100, with 15 points representing one standard deviation. This is a scoring convention, rather than an amount of intelligence counted directly. Interpreting a result requires the test, its norms and the procedure used to obtain it.
What a mean of 100 describes
A raw score can count correct answers or sum values defined by an instrument. Norming procedures support expressing performance on a reference scale. WAIS-5 technical documentation, for example, distinguishes subtest scores with a mean of 10 and standard deviation of 3 from composite scores with a mean of 100 and standard deviation of 15.
Seeing 100 on a screen is therefore insufficient. Ask what was transformed, using which data and for which population. Two instruments can display the same scale while measuring different aspects, or using different samples and administration conditions. Sharing units does not establish equivalent results.
What the standard deviation adds
Standard deviation describes spread. On a scale centred at 100 with a standard deviation of 15, 115 is one standard deviation above the centre and 85 is one below. This illustrates the scale’s arithmetic; it assigns neither score to a person taking this pilot.
If an ideal normal distribution is also assumed, its mean equals its median. Applying that mathematical shape to data requires justification. It does not establish that any collection of online correct-answer totals follows a normal distribution or that its extremes are estimated equally precisely.
Why a raw total cannot be converted by guesswork
Imagine two workbooks containing 20 problems each. Participants solve almost everything in one and almost nothing in the other. A total of 12 counts the same number of correct answers but does not describe the same position in both groups. Assigning that total an attractive IQ-scale number does not resolve the difference.
Subtracting a visitor average and dividing by its standard deviation does not turn visitors into a representative sample either. It may describe that group under specified rules; interpreting it for a country’s adults or a global population still needs justification. Correct arithmetic and a relevant comparison are different requirements.
A country average is not a person’s score
Searches for average IQ can mix norming scales, research sample means and country rankings. These are different kinds of information. Assessing a comparison requires knowing how people were selected, which versions were used and whether conditions support comparison. A table without that information cannot adequately answer the question.
You should not infer an individual’s score from their country, language or group. This website publishes no country ranking and does not adjust correct answers by origin. It applies the same complete-solution scoring rule to the pilot form and explains that it has no population norms of its own.
Questions to ask about a professional report
Find the test name and version, date, reference population, administration conditions and explanation of uncertainty. If an interval is reported, ask what it means for that instrument. Avoid treating a few points of difference as a definitive finding without this information.
Here, the report shows correct answers out of 22 tasks, responses, omissions and duration. The result appears on screen without requesting email. This guide explains a scale used elsewhere; it does not add an IQ conversion to the activity result.
Frequently asked questions
Does an IQ of 100 mean 100% correct?
No. It is a value on a reference scale. The percentage of tasks answered correctly describes a different quantity and cannot be identified with IQ.
Do all tests use exactly the same scale?
Do not assume they do. Check the manual: Even within one battery, subtests and composite scores can use different scales.
Sources you can check
Educational content by Sator editorial; it is not a professional assessment or clinical review. Commercial examples are not hands-on reviews. How we prepare these guides.