Quote from praetorian2:
I am not sure I agree with that fully. Take a fund trading lots of options. They may just slowly bleed premium, yet show little risk. I really think that in most cases, Sharpe just shows volatility and not directional volatility.
With daily level Sharpe, the hidden "account wipe out type of equity swing" will show up - just apply it on real cases you will see
We've seen this type of option model that reports Sharpe of 5+ based on monthly data and ended up reporting 0 when properly calculated based on daily data.
The key is that the volatility on the equity is huge on a daily basis when the portfolio is fully leveraged. The slowly bleed premium swing wildly (e.g 0.1 goes 0.05 then back to 0.1) in terms of % change.
Why then monthly data looks good? Because the options expired before the months ended
One of the requirements of proper Sharpe calculation is that the resolution of the equity changes must be finer than the average position length. This important requirement is often ignored.
For example, if you day trader, the better Sharpe ratio should be 5 min or even 1 min based. Use daily Sharpe can only give you an idea of the best scenerio.
For average mutual funds, they use monthly data because their holding period of a security is usually longer than a month.
That becomes a loophole when applying the same standard to hedge funds as they trade way more frequently and the holding period of a position is way shorter than a month.
A non-option example is the Oddball system. If using monthly Sharpe, it is pretty impressive but based on daily Sharpe, it is way lower. The daily equity swing of the Oddball is so huge I think not many individuals can take such heat
