Symmetry plots can be used to assess whether sample data comes from a symmetric distribution. Many statistical procedures assume that data come from a normal distribution. However, many procedures are robust to violations of normality, so having data from a symmetric distribution is often sufficient. Other procedures, such as nonparametric methods, assume symmetric distributions rather than normal distributions. Therefore, a symmetry plot is a useful tool in many circumstances.

You want to determine the quality of the process of filling cereal boxes with the correct weight of product. Before doing any further analysis, you would like to determine whether or not the sample data come from a symmetric distribution.

Data: CerealBox.MTW (available in the Sample Data folder).