Data Analysis with Microsoft Excel: Updated for Office 2007

Chapter 5 Probability Distributions 195

2 Click the down spin button next to the mu box to change the value

of m back to 0.

3 Click the down spin button next to the sigma box to reduce the value

of s to 0.3. The distribution tightens around the center.

4 Click the up spin button next to the sigma box to increase the value of

s to 1.5. The distribution spreads out, indicating a wider range of

probable values.

Figure 5-10 shows the normal curve for a variety of m and s values.

μ = 0, = 1 μ = 0, = 0.5 μ = 0, = 1.5

Figure 5-10
The normal
distribution
for varying
values of

5 Examine other values of m and s to continue to explore how those

changes affect the distribution. Close the Distributions workbook

without saving any changes when you‘re fi nished.

In the normal distribution, about 68.3% of the values lie within 1 s, or

1 standard deviation, of the mean m. About 95.4% of the values lie within

2 standard deviations of the mean, and more than 99% of the values lie

within 3 standard deviations of the mean. See Figure 5-11.