Safety First Ratio following, variation, practice, expected

ASSet_MANagemen

In the book Roy's Safety First is defined as:

RSF = (Rp - Rmar) / (std. dev portfolio)

However, I was just doing some Schweser practice problems and they defined it in the following way in the answer:

"The safety first ratio can be calculated as the expected portfolio return minus 2 standard deviations."

-----
Is there a variation of the Safety First ratio that I didn't read?