To ensure that your results are valid, consider the following guidelines when you collect data, perform the analysis, and interpret your results.
You must have numeric data, such as the weights of packages.
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.
A sample size that is less than 20 may not provide enough power to detect significant differences between your sample data and the normal 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.