Mate it's your honours research.... what is your scope? What are you trying to achieve?
From a safety/quality point of view, I would be targetting the people who are working as a pilot, even if only part-time, as their fatigue (or otherwise) affects the quality of the product and the safety of the client.
I would be especially interested in casual pilots and part-time pilots, and the interaction between their flying employment and non-flying employment demands.
If you are interested in training outcomes, student pilot fatigue is relevant... but you would be asking very different questions, which would be less relevant to working pilots.
By "General Avation Pilots" I presumed you meant pilots
working in non-airline non-military fields... which is what GA encompasses.