Suppose I want to estimate an equity beta with the goal of eventually finding WACC. I have access to monthly prices for my stock (as well as overall market returns) going back 40 years to its IPO as a young firm. Should I use 40 years of returns for my regression? Yes. O Probably not. A statistics theorem sholms that results of any regression become less reliable with more than about 200 data points. Probably not. The risk of my firm now might be substantially different from what it was 40 years ago Both B and Care true