Glossary
Ceiling effect
Definition
A ceiling effect happens when a test does not have enough hard items to tell high scorers apart. Many strong performers bunch up near the top possible score, so the test cannot say how far above that point they really are. A floor effect is the same problem at the bottom.
Want your own number? The test is 25 visual puzzles, about 12 minutes, no sign-up.
Why it matters for IQ scores
Most tests are designed to measure the middle of the scale well, where most people are. Out in the tails, the normal curve thins quickly: from the curve, about 1 in 740 people score 145 or higher and about 1 in 32,000 score 160 or higher. A test needs very hard items, and many of them, to locate someone up there, and few tests have enough.
An example
On a 25-item test, someone who answers all 25 correctly has shown that they are above the hardest items, but not by how much. A scoring model can still give an estimate, but its standard error is large. That is why IQ Octopus caps its scale at 160 and shows a wider range for very high estimates.
Common confusions
A ceiling is not a statement that nobody is smarter than the top score. It is a limit of the instrument. Claims of extremely high IQs from short tests deserve extra caution for this reason. See item difficulty, confidence interval, what an IQ of 160 means and what is the highest possible IQ score?
Try one · Logical Reasoning
Which tile completes the second pair?
Tap the option you think is right, or show the answer.
Show the answer
The missing panel shows a small solid square, with small solid shapes: a circle at the top-right corner and a circle at the top-left corner (option 3).
How to solve it
- Compare the first two panels and name exactly what changed.
- The main shape and the small shapes swap forms: the main shape takes the form of the small ones, and the small ones take the form of the main shape.
- Nothing else changes.
- Apply the same change to the third panel: a small solid circle, with small solid shapes: a square at the top-right corner and a square at the top-left corner.
- So the missing panel shows a small solid square, with small solid shapes: a circle at the top-right corner and a circle at the top-left corner.
That was 1 puzzle. The full test has 25.