# Fixed Effects

Use this field to specify effects by which to model the mean of the response variable.

This option is available only when the Response Type is an incidence density.

Note: Do not specify the treatment variable as it is automatically included.

Observe the following conventions in this field:

| • | Separate the effects with spaces.

| • | Use an asterisk (*) to create interactions. For example, assuming A and B are listed as Class Variables, specifying A B A*B constructs a two-way ANOVA model.

| • | Use a vertical bar (|) to create main effects and interactions. For example, A|B|C is the same as A B A*B C A*C B*C A*B*C.

| • | Use an at-sign (@) following the use of vertical bars to remove interaction terms. For example, A|B|C@2 removes the three-way interaction term from A|B|C.

### To Specify Fixed Effects:

| 8 | Make sure that either Incidence density based on first event only or Incidence density based on all events is selected as the Response Type.

| 8 | Enter the fixed effects in the Fixed Effects field.

| 8 | For example, to group the data from different study sites (listed in the SITEID column) into levels, type SITEID in the text box, as shown below:

| 8 | If you change your mind and would like to reset the field, click .