For the graph to represent your data most effectively, consider the following guidelines.
- The sample size should be greater than 20
- When you create a probability plot, a sample size that is less than 20 may not provide enough power to detect significant differences between your sample data and the specified theoretical distribution. However, use caution with very large sample sizes, as they may provide too much power. When a test has too much power, small and possibly meaningless differences between your sample data and the theoretical distribution appear to be significant.
- 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.