Data Analysis with Microsoft Excel: Updated for Office 2007

Chapter 5 Probability Distributions 215

Note that if you want to view the histogram with different bin values under

different sample sizes, you can deselect the Constant Bin Values checkbox.

When the bin values are the same, you can compare the spread of the data

from one histogram to another because the same bin values are used for all

charts. Deselecting the Constant Bin Values checkbox fi ts the bin values to the

data and gives you more detail, but it’s more diffi cult to compare histograms

from different sample sizes. You can also “freeze” the y axis to retain the y

axis scale from one sample size to another, making it easier to compare one

chart with another. To scale the y axis to the data, unselect the Freeze the Y-

Axis checkbox.

Now that you’ve viewed the sampling distribution for the standard nor-

mal, you’ll choose a different distribution from the list. Another commonly

used probability distribution is the uniform distribution. In the uniform

distribution, probability values are uniform across a continuous range of

values. The probability density function for the uniform distribution is

Uniform Probability Density Function

f 1 y 25

1

b 2 a

2 `, b ,` , 2` , a , b

where b is the upper boundary and a is the lower boundary of the distribu-

tion. Figure 5-25 displays the Uniform distribution where a 5 2 2 and b 5 2.

upper boundary

lower boundary

Figure 5-25
The uniform
probability
distribution

The mean m and standard deviation s for the uniform distribution are

m5

b 1 a

2

s5

b 2 a

" 12

Thus if a 5 2 2 and b 5 2, m 5 0 and s (^5 4) /" 12 5 1.1547.