Frank,
To answer your question then, given the metrics you enumerated I would think that a random sample with a mix of gamblers, potential gamblers and non-gamblers would be more interesting. If the participants can be categorized into groups, that would provide some additional information on what impact formerly learned concepts about gambling have on the study results.
To answer your question then, given the metrics you enumerated I would think that a random sample with a mix of gamblers, potential gamblers and non-gamblers would be more interesting. If the participants can be categorized into groups, that would provide some additional information on what impact formerly learned concepts about gambling have on the study results.