Explain how a stock's historical mean return is conceptualized as its expected value in portfolio risk analysis.

Question:

Explain how a stock's historical mean return is conceptualized as its "expected value" in risk analysis.
Portfolio
A portfolio is a grouping of financial assets such as stocks, bonds, commodities, currencies and cash equivalents, as well as their fund counterparts, including mutual, exchange-traded and closed funds. A portfolio can also consist of non-publicly...