Is 36 months considered a long or short period for calculating a company's Beta?

Yahoo Finance calculates a company's beta by looking at its trailing 36 months returns. My friend argues that's a short period of time given the overall age of the stock market, but I think 3 years is a long time for looking at just one metric of a company's riskiness.

Submitted October 18, 2016 at 12:48PM by DinoCapital http://ift.tt/2eiYMkr