, , , , , , ,
The number of classes can be estimated using the rounded output of Sturges' rule, , where is the number of classes and is the number of items in the data set.
Select classes for this example.
Find the data range by subtracting the minimum data value from the maximum data value. In this case, the data range is .
Find the class width by dividing the data range by the desired number of groups. In this case, .
Round up to the nearest whole number. This will be the size of each group.
Start with and create groups of size .
Determine the class boundaries by subtracting from the lower class limit and by adding to the upper class limit.
Draw a tally mark next to each class for each value that is contained within that class.
Count the tally marks to determine the frequency of each class.
The relative frequency of a data class is the percentage of data elements in that class. The relative frequency can be calculated using the formula , where is the absolute frequency and is the sum of all frequencies.
is the sum of all frequencies. In this case, .
The relative frequency can be calculated using the formula .
Simplify the relative frequency column.
Multiply every relative frequency by to get the percentage frequency.
Simplify the Percentage column.