How often are passenger oxygen masks deployed? In commercial passenger aviation, how frequent (or infrequent) is the case that oxygen masks deploy?

Please include links to statistics.
Very, very rare, probably in the range of sinlge digits per 100,000 flights (for major first-world airlines, perhaps higher elsewhere).

I'll try to get you a more numeric answer tomorrow.

Posting an answer now so that I can edit it, evem if the question gets closed between now and then.

"Opinion based", horsefeathers!