Hello everyone, hope you are well.
I am planning to use a Generalized Linear Model in SPSS. I would like to add gender to the model as a covariate, however from what I have read, only continuous variables can be added to the covariates box. I would like to know if I can add gender as a factor in a Generalized Linear Model, even though it is a variable that I want to adjust the model for. I also have continuous covariates (age and income) that I want to add to the model. My independent variable is Health Profile which I will add as a factor.
I have read that a categorical covariate can be added if it is coded as a dummy variable but I am unsure of which approach is best. The covariates gender, age and income are important in the context of my research.
Kind regards,
Hana
Hello Hana,
A dichotomous categorical variable may be used as a covariate without further modification (as nominal values of 0,1 or 1,2 for the respective levels will suffice, and there is only one step in the "scale"). For categorical variables having more than two levels (and not ordinal), you'd have to recast the k-level variable into k - 1 dummy variates (or similar), and enter these as a set of covariates to capture all of the information associated with the categorical variable.
Good luck with your work.
Hello Hana,
A dichotomous categorical variable may be used as a covariate without further modification (as nominal values of 0,1 or 1,2 for the respective levels will suffice, and there is only one step in the "scale"). For categorical variables having more than two levels (and not ordinal), you'd have to recast the k-level variable into k - 1 dummy variates (or similar), and enter these as a set of covariates to capture all of the information associated with the categorical variable.
Good luck with your work.
The GENLIN command allows you to treat categorical explanatory variables as "factor" variables, with no need to generate your own dummy (or indicator) variables. In the command syntax, quantitative explanatory variables (or "covariates" in SPSS terminology) follow the keyword WITH and factor variables follow the keyword BY. You can find examples in the Command Syntax Reference Manual.
Yes, you can use categorical variables as independent variables. Click "analyze" --> "generalized linear models" --> "generalized linear models" --> (a separate window pops up). From there, you will see several tabs (type of model, response, predictors, model, etc.). Simply follow the tab from left to right and select appropriate family/link function, response (dependent) variable, predictors (independent variables), model. You would move categorical covariates to "factor" section and continuous covariates to "covariates" under the "predictors" tab. You would then select your model (main or interaction), then choose estimation/statistics to run your model.
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