To compare my stock portfolio generator with managed funds performance, I want to calculate the Sharpe Ratio of my historic portfolios with the numbers found on the fund company web sites or in financial portals. However, I could not find a specification of their calculations. I also emailed MorningStar to no avail.
Question 1: What exactly should be used for risk-free interest? I can use the 12M USD LIBOR but it is at least 1% below the risk-free interest a private investor can expect (I am looking for a one year performance, i.e. hold all stocks exactly one year).
Question 2: I am using LOG10(day /day before) returns for the stdev calculation, but for the return calculation I use last portfolio value - first portfolio value - 1.0. That is probably total bogus and makes my numbers look too good but since I could not find a reference... I might as well use geometric averages or dollar amounts as was suggested in one answer to a similar question here, but what is the official way of doing it?
So my main question is: how exactly do the fund companies calculate the Sharpe Ratio? I also heared the opinion that they do it this way or the other, whatever suits. But that would make the Sharpe Ratio worthless for comparing fund performance, so there must be one accepted method?!