You can add covariates if you would like to see how the results differ between subgroups of studies or if you want to include these covariates in your regression analyses (see Analysis graphs in diagnostic reviews). It may be wise to define your covariates before you start entering data. The covariates can then be entered simultaneously with the rest of the data (instead of going back and adding covariate data for the studies afterwards).
To add a covariate
Right-click the Covariates heading in the outline and choose Add Covariate.
The Add Covariate Wizard opens.
Enter the name of the covariate and a more detailed description.
Select whether you want to enter the data for this covariate at the study or test level.
Select whether it is a dichotomous or a continuous covariate.
Choose a type of covariate data and click Next.
There are two data types:
For continuous covariates, you may enter a default value.
For categorical covariates, you must define the different categories. Click Add to create a category. When all categories have been created, use the pull-down list to specify the default category.
If you would like to be able to show subgroups on the SROC plot, you should choose the categorical data.
Click Finish.
The covariate appears in the outline . You can now enter the data of the covariates in the data tables by test or the data tables by study.
Note: Although you may want to explore the effect of certain quality items and would like to add these as covariates, these need not to be entered under this heading. The quality items are already under the Characteristics of Included Studies.
You can enter and modify information about the covariates you would like to add via the covariate properties windows.
To modify covariate properties
Right-click the covariate and choose Properties.
The Covariate Properties window opens to the General tab.
Change the short name or full name of the test as needed.
Select whether you want to add the values for the covariate
for all studies and for one test or
per study for all tests.
To specify the type of covariate (continuous or categorical), click the Type tab .
For continuous covariates, you must enter a default value.
For categorical covariates, you must define the different categories. Click Add to create a category. When all categories have been created, use the pull-down list to specify the default category.
Click OK.