Even though I understand that "pá" is a vocative expression and that it's also typical European Portuguese usage, I have some doubts about it:
- What's the etymology of "pá"? Is it a short form for another word?
- I've been to Portugal several times but I heard it only from a few persons who seem to use it all the time. Was this a coincidence or is it really unusual? Can it be taken as an indicator of social class or educational background?
- Is it informal and unlikely to be heard during a lecture or formal speech?
- Is there a region where one is more likely to hear it? (e.g. north x south)