Data considerations for Boxplot

For the graph to represent your data most effectively, consider the following guidelines.

The sample size should be approximately 20 or greater
A boxplot works best when the sample size is at least 20. If the sample size is too small, the quartiles and outliers shown by the boxplot may not be meaningful. If the sample size is less than 20, consider using an Individual value plot instead.
The sample data should be selected randomly
In statistics, random samples are used to make generalizations, or inferences, about a population. If your data were not collected randomly, your results may not represent the population.