Data Analysis with Microsoft Excel: Updated for Office 2007

160 Fundamentals of Statistics

The most common measure of variability depends on the deviation of

each data value from the sample average. For each data value xi, calculate

the deviation di, which is the difference between sample value and the sam-

ple average, or

di 5 xi 2 x

Some of these deviations will be negative (where the data value is less than

the mean), and some will be positive, so we cannot simply take the average

of the deviations because the positive and negative values would cancel each

Figure 4-21

Distribu-

tions with

different

variability

but the

same range

range