Here is the formula used: Sortino is same as Sharpe except its denominator is the annualized downside deviation, which only uses
monthly returns falling below TBill
average, as shown here: Finally, Martin, which uses same numerator as Sharpe and Sortino, excess
return relative to TBill, but it uses the Ulcer Index (UI) for the denominator, which is the square root of the mean of the squared percentage draw downs in value.