The Efficiency of the Market Portfolio
In the CAPM, the marginal utilities of all securities with respect to the
holdings in the market portfolio are equal when evaluated using the societal
risk tolerance. This is sufficient for the efficiency of the market portfolio. It
is also necessary if the market portfolio is to be efficient for an investor with
the societal risk tolerance.
More generally, for the market portfolio to be efficient, the marginal
utilities of all securities measured relative to the market portfolio must be
equal when evaluated using some positive risk tolerance. This follows from
the fact that the market portfolio includes positive amounts of every security,
hence all securities will be in such a portfolio.
For this condition to be met, there must be a linear relationship between
security expected returns and their beta values24. With restrictions on
negative holdings this may not be the case, due to the influences of the z im
values25. Hence the market portfolio may be inefficient. Of course, the
The Efficiency of the Market PortfolioIn the CAPM, the marginal utilities of all securities with respect to theholdings in the market portfolio are equal when evaluated using the societalrisk tolerance. This is sufficient for the efficiency of the market portfolio. Itis also necessary if the market portfolio is to be efficient for an investor withthe societal risk tolerance.More generally, for the market portfolio to be efficient, the marginalutilities of all securities measured relative to the market portfolio must beequal when evaluated using some positive risk tolerance. This follows fromthe fact that the market portfolio includes positive amounts of every security,hence all securities will be in such a portfolio.For this condition to be met, there must be a linear relationship betweensecurity expected returns and their beta values24. With restrictions onnegative holdings this may not be the case, due to the influences of the z imvalues25. Hence the market portfolio may be inefficient. Of course, the
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