A Nobel Memorial Prize winning economist who devised the modern portfolio theory in 1952.  Markowitz's theories emphasized the importance of portfolios, risk, the correlations between securities and diversification. His work changed the way that people invested.

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Prior to Markowitz's theories, emphasis was placed on picking single high-yield stocks without any regard to their effects on portfolios as a whole. Markowitz's portfolio theory would be a large stepping stone towards the creation of the capital asset pricing model.

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