Modeling and Multivariate Methods - SAS

226 Performing Logistic Regression on Nominal and Ordinal Responses Chapter 7
Stacking Counts in Multiple Columns
Stacking Counts in Multiple Columns
Data that are frequencies (counts) listed in several columns of your data table are not the form that you need
for logistic regression. For example, the Ingots2.jmp data table in the data folder (see Figure 7.26) has
columns Nready and Nnotready that give the number of ready and number of not ready ingots for each
combination of Heat and Soak values. To do a logistic regression, you need the data organized like the table
in Figure 7.27.
To make a new table, suitable for logistic regression, select the Stack command from the Tables menu.
Complete the Stack dialog by choosing Nready and NNotReady as the columns to stack, and then click OK
in the Stack dialog. This creates the new table in Figure 7.27. If you use the default column names, Label is
the response (Y) column and Data is the frequency column.
The example in the section “Introduction to Logistic Models” on page 199, shows a logistic regression using
a sample data table Ingots.jmp. It has a frequency column called count (equivalent to the Data column in
the table below) and a response variable called Ready, with values 1 to represent ingots that are ready and 0
for not ready.
Figure 7.26 Original Data Table