Data considerations for Graphical Summary

To ensure that your results are valid, consider the following guidelines when you collect data, perform the analysis, and interpret your results.

The data must be numeric: You must have continuous data, such as the weights of packages, or discrete data, such as the number of complaints. If you want to summarize samples of count data, use Tally Individual Variables.
The sample data should be selected randomly: In statistics, random samples are used to make generalizations, or inferences, about a population. If your data are not collected randomly, your results may not represent the population. For more information, go to Randomness in samples of data.
Collect a medium to large sample of data: Samples that have at least 20 observations are often adequate to represent the distribution of your data. However, to better represent the distribution with a histogram, some practitioners recommend that you have at least 50 observations. Larger samples also provide more precise estimates of the process parameters, such as the mean and standard deviation.