portfolioteoria

Portfolioteoria, also known as modern portfolio theory (MPT), is a mathematical framework for assembling a portfolio of assets such that the expected return is maximized for a given level of risk. It was developed by Harry Markowitz in 1952. The core idea of portfolioteoria is that investors can construct a portfolio of assets that offers a better risk-return trade-off than any individual asset within the portfolio. This is achieved by diversifying investments across different asset classes that are not perfectly correlated.

The theory relies on the concept of diversification to reduce unsystematic risk, which is the risk specific to an individual company or industry. By holding a variety of assets, the losses in one asset can be offset by gains in another, leading to a smoother overall return for the portfolio. Portfolioteoria quantifies risk primarily through volatility, typically measured by standard deviation. It seeks to identify the "efficient frontier," which represents the set of optimal portfolios that offer the highest expected return for a defined level of risk or the lowest risk for a given expected return.

Key inputs for portfolioteoria include the expected returns of individual assets, their volatilities, and the correlations between them. By analyzing these factors, investors can determine the optimal allocation of their capital among different assets to achieve their specific investment goals and risk tolerance. While influential, portfolioteoria has also faced criticisms, particularly regarding its reliance on historical data to predict future returns and its assumption of rational investor behavior.