Explain non diversifiable risk? How is it measured?
Unless the returns of one-half the assets into a portfolio are entirely negatively correlated along with the other half-that is extremely unlikely-some risk will remain after assets are combined in a portfolio. The degree of risk which remains is non diversifiable risk, the part of portfolio's entire risk which can't be eliminated by diversifying.
Non diversifiable risk is measured by a term termed beta (β). The final group of diversified assets, the market, contain a beta of 1.0. The betas of portfolios, and individual assets, relate their returns to those of the total stock market. Portfolios along with betas higher than 1.0 are relatively more risky in compare of the market. Portfolios along with betas less than 1.0 are relatively less risky than the market. (Risk-free portfolios have a beta of zero.)