Ask HN: Percent of employees that benefit financially from equity offers?

Title says it all. Equity offers are a very common thing in tech. I don't personally know anyone who has made money from equity offers, though nearly all my colleagues have received them at some point.

Does anyone have real data on how many employees actually see financial upside from equity grants? Are there studies or even anecdotal numbers on how common it is for non-executives/non-founders to walk away with any money? Specifically talking about privately held US startups.