Sharpe ratio calculation

[cnd]

Schweser Study Notes book 1, Assigned Reading 7, Statistical Concepts and Market Returns, Comprehensive Problems, page 189:
Problem 1.J.
Problem: What is the Sharpe ratio for an investment in the Nopat Fund over the five years from 2000-2004?
My questions:
1. How / why did they decide to use sample standard deviation here instead of population standard deviation?
2. How / why did they decide to use arithmetic mean return on the portfolio for these purposes, as opposed to some other return measure, such as the geometric mean?

 

[madanalyst]

sample stdev bcoz the returns that they have selected is a sample from the population of all the returns of the fund ..

arithmetic mean is expected return, geo mean is more like a growth rate and do not considered as expected return ...