The following equation shows how to calculate the standard deviation of grouped data in a frequency distribution.

where:
*f*_{i} = the number of data values in each frequency class
*m* = the number of classes *m*
*n* == the total number of values in the data set

The following table is a frequency distribution that represents the number of times each child in Debbie’s 3-year-old preschool class needs a “potty break” in a day.

In this example, *m* = 5 and *n* = 30. From Chapter 4, we know the mean ...

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