Data Analysis with Microsoft Excel: Updated for Office 2007

Chapter 5 Probability Distributions 209

The distribution of the sample averages looks normal and, in fact, is nor-

mal. The distribution is centered at 0, as you would expect for averages

based on samples taken from the standard normal distribution. The distri-

bution differs from the standard normal in one respect: The sampling dis-

tribution is much narrower around the mean. Most of the standard normal

values lie between 2 2 and 2, but here most of the values lie between 2 0.5

and 0.5. Apparently the s for the sampling distribution of the sample aver-

age is smaller than the value of s for a standard normal. To verify this, cal-

culate descriptive statistics for the sample averages.

To calculate descriptive statistics for the sample averages:

1 Return to the worksheet containing the sample average values.

2 Click Descriptive Statistics from the StatPlus menu and then click

Univariate Statistics.

3 Click the Input button, click the Use Range References option but-

ton, and select the range P1:P100. Deselect the Range Includes a

Row of Column Labels checkbox. Click the OK button.

4 Click the Summary tab and click the Count and Average checkboxes.

5 Click the Variability tab and click the Std. Deviation checkbox.

Figure 5-21
Histogram
of sample
averages