ER - (2xSD) vs. Roy Safety First given, think, guide, either, criteria

yuoska

When, in IPS, given a "can't lose more than x%" criteria, i have seen this done by either using RSF, or exp ret less 2 X Standard Dev.

Anybody have any idea when to use which, if they don't guide you (2007 i think it was told you to use the 2x SD version)