You're exploring a very complicated subject. It's a puzzle with many moving parts. Maybe too many.
I'm not in your search demographic so I can't take your survey but have one question: A shortage of
what pilots ? I assume you'll look at categories other than airline pilots since other categories impact airline pilot supply. Climb150 has named one very big factor contributing to the current situation in the USA.
Here's one organizational opinion:
Pilot Supply - ALPA