Chapter Contents |
Previous |
Next |

Descriptive Statistics |

You can examine the distributional properties of your data with the Distributions task. This task enables you to produce descriptive statistics for the variables, test the fit of several distributions to your data, and examine displays such as histograms and probability plots. In this task, interest lies in examining the birth and infant mortality rates for each region.

- Select
**Statistics****Descriptive****Distributions**... - Select birth and death as the analysis variables.
- Select region as the classification variable.

Figure 7.12 displays the Distributions main dialog with the preceding variable specifications.

The default analysis provides moments, quartiles, and measures of variability.

- Click on the
**Plots**button. - Select
**Box-&-whisker plot**. - Select
**Histogram**. - Click
**OK**.

Figure 7.13 displays the Plots dialog.

- Click on the
**Fit**button in the main dialog. - Select
**Normal**.

By default, parameter values are calculated from the data when you fit
the normal distribution. If you want to enter specific parameter
values, click on the down arrow (displayed in Figure 7.14) and
select **Enter values**. For the lognormal, exponential, and
Weibull distributions, you can specify that parameters be calculated
by maximum likelihood estimation (MLE), or you can enter specific
parameter values.

- Click
**OK**.

When you have completed your selections, click **OK** in the
main dialog to perform the analysis. The
results are presented in the project tree displayed in Figure 7.15.

The Moments and Quantiles output provides summary information for each variable. Figure 7.16 displays the output labeled Fitted Distributions of Bthdth92, which summarizes how closely the normal distribution fits each variable, by region.

Based on the test results displayed in Figure 7.16, the null
hypothesis that the variable birth is normally distributed
cannot be rejected at the level of significance
(*p*-values for all tests are greater than
0.15). The same is true for the variable death
except for the southern region (region=`S'). The hypothesis is
rejected at
the level of significance
for the death rate in the southern region.

Two sets of box plots and four sets of histograms are also produced.
A single box-and-whisker plot is created for each of the two
variables.
The box-and-whisker plot for the variable birth is
displayed when you double-click **Box Plot of BIRTH** in the project
tree.

Two histograms are created for each variable. Each graphic contains a histogram for two levels of the classification variable region. The first histogram contains the information for the midwestern and northeastern regions (region=`MW' and region=`NE'), as displayed in Figure 7.17. The second histogram (not shown) contains the information for the southern and western regions (region=`S' and region=`W').

The normal curve overlaid on the histogram displayed in Figure 7.17 is the result of requesting a normal distribution fit in the Fit dialog (Figure 7.14). The statistical details of the fit are located in the output labeled Fitted Distributions of Bthdth92, which also includes the details of the fit for the variable death.

Chapter Contents |
Previous |
Next |
Top |

Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.