Section 3.1 Summary

1. Measures of center are introduced in Section 3.1. The sample mean represents the sum of the data values in the sample divided by the sample size . The population mean represents the sum of the data values in the population divided by the population size . The mean is sensitive to the presence of extreme values.
2. The median occupies the middle position when the data are put in ascending order and is not sensitive to extreme values.
3. The mode is the data value that occurs with the greatest frequency. Modes can be applied to categorical data as well as numerical data but are not always reliable as measures of center.
4. The skewness of a distribution can often tell us something about the relative values of the mean and the median.