bboo

Sometimes if the question say "I don't want my portfolio fall below -10%"

We use Roy = [E(R) - (-10)]/STD to compare which portfolio is higher.

In CFAI textbook, Vol 2, P.136. The question stated that a worst-case return of -10% would be acceptable.

They use E(R) - 2*STD to calculate the worst-case return for each portfolio and see which portfolio has worst-case return > -10%.

My question is..
The statement "I don't want my portfolio fall below -10%" and "the worst-case return of 10% looks are acceptable" looks similar. How do we distinguish which one to use ? (Worst case return or Roy, both are downside risk measures).