Using gret l for Principles of Econometrics, 4th Edition

Sessions

Gretl also has a “session” concept that allows you to save models, graphs, and data files into a common “iconic” space. The session window appears below in Figure 1.12. The session window is very handy. It contains icons that give you immediate access to information about the data set, that opens the edit data window, that display any scalars you have computed, summary statistics, correlations and any notes you may want to make.

Objects are represented as icons and these objects can be saved for later use. When you save your session, the objects you have added should be available again when you re-open the session. To add a model to your session, use the File>Save to session as icon option from the model’s pull-down menu. To add a graph, right click on the graph and choose the option save to session as icon. If you want to save the results in your session, don’t forget to do so; right click on the session window and choose Save session or from the main gretl window, select File>Session files>Save session as shown below in Figure 1.13.

Once a model or graph is added, its icon will appear in the session icon view window. Double­clicking on the icon displays the object, while right-clicking brings up a menu which lets you display or delete the object. You can browse the dataset, look at summary statistics and correlations, and save and revisit estimation results (Models) and graphs.

The model table is a way of combining several estimated models into a single table. This is very useful for model comparison. From the gretl manual ((Cottrell and Lucchetti, 2011, pp. 16-17)):

In econometric research it is common to estimate several models with a common depen­dent variable the models contain different independent variables or are estimated using different estimators. In this situation it is convenient to present the regression results in the form of a table, where each column contains the results (coefficient estimates and standard errors) for a given model, and each row contains the estimates for a given variable across the models.

In the Icon view window gretl provides a means of constructing such a table (and copying it in plain text, LTEX or Rich Text Format). Here is how to do it:

1. Estimate a model which you wish to include in the table, and in the model display window, under the File menu, select Save to session as icon or Save as icon and close.

2. Repeat step 1 for the other models to be included in the table (up to a total of six models).

3. When you are done estimating the models, open the icon view of your gretl session, by selecting Icon view under the View menu in the main gretl window, or by clicking the session icon view icon on the gretl toolbar.

4. In the Icon view, there is an icon labeled Model table. Decide which model you wish to appear in the left-most column of the model table and add it to the table,

either by dragging its icon onto the Model table icon, or by right-clicking on the model icon and selecting Add to model table from the pop-up menu.

5. Repeat step 4 for the other models you wish to include in the table. The second model selected will appear in the second column from the left, and so on.

6. When you are finished composing the model table, display it by double-clicking on its icon. Under the Edit menu in the window which appears, you have the option of copying the table to the clipboard in various formats.

7. If the ordering of the models in the table is not what you wanted, right-click on the model table icon and select Clear table. Then go back to step 4 above and try again.

In section 6.4 you’ll find an example that uses the model table and a Figure (6.13) that illustrates the result.