I have conducted a survey which asks respondents to indicate the informational sources regarding a product. There are 8 information sources (e.g., internet, newspaper, brochure and so on) and people can choose more than one source.
I want to use information source a predictor variable in a multiple regression. However, because people can choose more than one information source, it does not seem possible to to treat it as a single categorical variable.
How can a categorical variable where respondents can choose more than one response be used as a predictor in multiple regression?