About the Analysis of Means Task :: SAS(R) Studio 3.5: Task Reference Guide

Mean Chart

The mean chart shows the deviation of the mean for the groups identified by the Group variable.

Here is an example of a mean chart. For more information, see Example: Determine the Deviation of Label Positions.

Mean Chart with Boxes

You can choose to include box charts to show the deviation of the mean for each group.

Here is an example of a mean chart with boxes:

Proportion Chart

Proportion charts (also called p charts) are for group (treatment level) proportions.

A health care system administrator wants to compare cesarean section rates for a set of medical groups (Rodriguez 1996).

For the analysis, the administrator creates this p chart.

Each point on the p chart represents the proportion of C-sections for a particular group. For example, the value plotted for group 1A is 150/923=0.163. Because all the points fall within the decision limits, it can be concluded that the variation in proportions of C-sections across medical groups is strictly due to chance. By default, the decision limits shown correspond to a significance level of

alpha equals , 0.05. Click image for alternative formats.

. If you assume that all groups have the same proportion of C-sections, there is a 0.05 probability that one or more of the decision limits are exceeded purely by chance. The decision limits vary with the number of deliveries in each group, and the widest limits correspond to the group with the smallest number of deliveries.

Rate Chart

A rate chart (also called a u chart) is for group (treatment level) rates. The rate plotted on a u chart is the number or count of events that occur in a group divided by a measure of the opportunity for an event to occur.

A health care administrator wants to compare the admission rates for a set of clinics (Rodriguez 1996).

For the analysis, the health care administrator creates this u chart.

Each point on the u chart represents the rate of occurrence, computed as the count divided by the number of opportunity units. The points are displayed in the sort order for the group variable, ID. The chart shows that Clinics 1D, 1H, and 1M have significantly higher admissions rates, and Clinics 1N, 1T, and 3H have significantly lower admissions rates.

By default, the decision limits correspond to a significance level of

. If you assume that all clinics have the same rate of admissions, there is a 0.05 probability that one or more of the decision limits are exceeded purely by chance. The decision limits vary with the number of 1,000 member years for each clinic.