Question

How many classes are recommended in a histogram of a data set with less than 25 observations?

Answer 1

There is no mandatory requirement for the numbers of classes, but some formulas can be used for estimating this amount.

For examle, Sturgess formula: $k = log{\scriptscriptstyle 2}N +1$

Or the following formula

$k = \sqrt{N}$

In our case we receive the next values:

5.61

5

So, it is appropriate to make no more than 5-6 classes for such a sample. For example, if we sample size is 10 then it should be 3 classes.