General Model (Generalized Linear Models)

Select menu: Stats | Regression Analysis | Generalized Linear Models

Use this to use any of Genstat’s standard range of link functions and error distributions; these are selected using the Distribution and Link function dropdown lists. (If, however, you have a non-standard model, others can be defined by using the MODEL directive in command mode or by using the GLM procedure.) If you choose the negative binomial distribution, you must also specify a fixed value for the aggregation parameter (the parameter k in the formula for the variance in terms of the mean: v = m + m*m/k). You can choose a general power link, in which case you need to specify the exponent; the logratio link, log(m / (m+k)), also requires you to specify the parameter k.

After you have imported your data, from the menu select
Stats | Regression Analysis | Generalized Linear Models.
Fill in the fields as required then click Run.

You can set additional Options then after running, you can save the results by clicking Save.

Available data

This lists data structures appropriate for the input field which currently has focus. You can double-click a name to enter it in the input field.

Response variate

Specifies a variate for the response. This can be entered in directly or can be selected from those within the Available data list.

Maximal model

This lets you specify the most complicated model that you are likely to want to consider. It may be left blank, but this may lead to subsequent inability to compare models because of data that are missing for some explanatory variates but not for others.

Model to be fitted

The model to be fitted is specified by entering a model formula into the Model to be fitted field. The formula can involve both variates and factors which can be selected from the Available data list, and operators from the Operators list.

Distribution

List of available error distributions. If you select the Binomial distribution then you must supply the Binomial totals in the space provided. Alternatively, if you select the Negative binomial you must supply the Aggregation in the space provided or select the estimate aggregation parameter option.

Link function

Lists the available link functions. If you select the Power link function then you must supply the Exponent in the space provided. Similarly, if you select the Logratio link function then you must supply the Logratio in the space provided.

Binomial totals

For a binomial distribution, this specifies a variate which contains the number of units the response was obtained from. This values in this must be greater than or equal to the corresponding values in the response variate.

Operators

This provides a quick way of entering operators in the Model to be fitted formula. Double-click the required symbol to copy it to the current input field. You can also type in operators directly. See model formula for a description of each.

Action buttons

Run	Run the analysis.
Cancel	Close the dialog without further changes.
Options	Opens a dialog where additional options and settings can be specified.
Defaults	Reset options to the default settings. Clicking the right mouse on this button produces a shortcut menu where you can choose to set the options using the currently stored defaults or the Genstat default settings.
Save	Opens a dialog where you can save results from the analysis.
Predict	Lets you calculate predictions based on the current regression model.
Change model	This changes the current model by adding or dropping explanatory terms, thus enabling a sequence of models to be fitted and assessed. If you specified a Maximal model, all new terms must have appeared in that model. If you did not specify a maximal model and a term is introduced with a missing value for a unit previously used in the regression, the model sequence is interrupted and information will be available only for the current model (excluding that unit) and the new model.
Further output	Lets you display additional results and graphical output from the analysis.

Action Icons

	Pin	Controls whether to keep the dialog open when you click Run. When the pin is down the dialog will remain open, otherwise when the pin is up the dialog will close.
	Restore	Restore names into edit fields and default settings.
	Clear	Clear all fields and list boxes.
	Help	Open the Help topic for this dialog.