Strategic StudentSmall Numbers Reality Check
How much should you trust a rate built on a small group?
Enter the rate and the group size
The answer shows up here as you type.
Each figure is one student.
Next step
How this works
The likely range is a Wilson 95% score interval: the range that most likely holds the underlying rate, the one this group would show over many similar years. It is the method statisticians recommend for small groups and for rates near 0% or 100%, where the textbook plus-or-minus formula breaks down (Brown, Cai and DasGupta, 2001). Near 0% and 100% the range is lopsided, so the tool shows both ends instead of one plus-or-minus number.
- Under 10 students: too few to call. Look at the students, not the rate.
- Range 10 points wide or less: solid enough to plan on.
- Up to 22 points wide: use with care, directional only.
- Wider than that: too shaky to compare groups or judge a program on its own.
A percentage is turned into a whole number of students first (25% of 7 becomes 2 of 7, which is 28.6%), because a rate can only be built from whole students.
The caution is about comparing and judging. For a teacher looking at their own students, the count is complete, and acting on those students is always right. Several shaky years moving the same way tell you more than one sharp one.