The GLMPOWER Procedure

Error and Information Output

The Error column in the main output table explains reasons for missing results and flags numerical results that are bounds rather than exact answers.

The Info column provides further information about Error entries, warnings about any boundary conditions detected, and notes about any adjustments to input. Note that the Info column is hidden by default in the main output. You can view it by using the ODS OUTPUT statement to save the output as a data set and the PRINT procedure. For example, the following SAS statements print both the Error and Info columns for a power computation in a one-way ANOVA:

data MyExemp;
   input A $ Y1 Y2;
         1   10 11
         2   12 11
         3   15 11
proc glmpower data=MyExemp;
   class A;
   model Y1 Y2 = A;
      stddev = 2
      ntotal = 3 10
      power  = .;
   ods output output=Power;
proc print noobs data=Power;
   var NominalNTotal NTotal Dependent Power Error Info;

The output is shown in Figure 44.5.

Figure 44.5: Error and Information Columns

NominalNTotal NTotal Dependent Power Error Info
3 3 Y1 . Invalid input Error DF=0
10 9 Y1 0.557   Input N adjusted
3 3 Y2 . Invalid input Error DF=0 / No effect
10 9 Y2 0.050   Input N adjusted / No effect

The sample size of 3 specified with the NTOTAL= option causes an Invalid input message in the Error column and an Error DF=0 message in the Info column, because a sample size of 3 is so small that there are no degrees of freedom left for the error term. The sample size of 10 causes an Input N adjusted message in the Info column, because it is rounded down to 9 to produce integer group sizes of 3 per cell. The cell means scenario represented by the dependent variable Y2 causes a No effect message to appear in the Info column, because the means in this scenario are all equal.