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Beta Prof. André Farber SOLVAY BUSINESS SCHOOL UNIVERSITÉ LIBRE DE BRUXELLES

Measuring the danger of an individual resource The measure of danger of an individual resource in a portfolio needs to consolidate the effect of expansion . The standard deviation is not a right measure for the danger of an individual security in a portfolio. The danger of an individual is its methodical hazard or market chance, the hazard that can not be dispensed with through expansion. Keep in mind: the ideal portfolio is the market portfolio. The danger of an individual resource is measured by beta . The meaning of beta is: A.Farber Vietnam 2004

Beta Several understandings of beta are conceivable: (1) Beta is the responsiveness coefficient of R i to the market (2) Beta is the relative commitment of stock i to the change of the market portfolio (3) Beta demonstrates whether the danger of the portfolio will increment or reduction if the heaviness of i in the portfolio is somewhat altered A.Farber Vietnam 2004

Beta as an incline A.Farber Vietnam 2004

A m easure of efficient hazard : beta Consider the accompanying direct model R t Realized profit for a security amid period t A steady : an arrival that the stock will acknowledge in any period R Mt Realized profit for the market all in all amid period t A measure of the reaction of the arrival on the security to the arrival available u t An arrival particular to the security for period t (idosyncratic return or unsystematic give back)- an irregular variable with mean 0 Partition of yearly return into: Market related part ß R Mt Company particular section a + u t A.Farber Vietnam 2004

Beta - outline Suppose R t = 2% + 1.2 R Mt + u t If R Mt = 10% The normal profit for the security given the arrival available E[ R t | R Mt ] = 2% + 1.2 x 10% = 14% If R t = 17%, u t = 17%-14% = 3% A.Farber Vietnam 2004

Measuring Beta Data: past returns for the security and for the market Do straight relapse : slant of relapse = assessed beta A.Farber Vietnam 2004

Decomposing of the difference of a portfolio How much does every benefit add to the danger of a portfolio? The difference of the portfolio with 2 unsafe resources can be composed as The fluctuation of the portfolio is the weighted normal of the covariances of every individual resource with the portfolio. A.Farber Vietnam 2004

Example A.Farber Vietnam 2004

Beta and the deterioration of the fluctuation The change of the market portfolio can be communicated as: To figure the commitment of every security to the general hazard, isolate every term by the difference of the portfolio A.Farber Vietnam 2004

Marginal commitment to hazard: some math Consider portfolio M . What happens if the division put resources into stock I changes? Consider a division X put resources into stock i Take first subordinate as for X for X = 0 Risk of portfolio increment if and just if: The peripheral commitment of stock i to the hazard is A.Farber Vietnam 2004

Marginal commitment to hazard: delineation A.Farber Vietnam 2004

Beta and minimal commitment to hazard Increase (sightly) the heaviness of i : The danger of the portfolio increments if: The danger of the portfolio is unaltered if: The danger of the portfolio diminishes if: A.Farber Vietnam 2004

Inside beta Remember the relationship between the connection coefficient and the covariance: Beta can be composed as: Two determinants of beta the connection of the security come back with the market the instability of the security in respect to the unpredictability of the market A.Farber Vietnam 2004

Properties of beta Two importants properties of beta to recollect (1) The weighted normal beta over all securities is 1 (2) The beta of a portfolio is the weighted normal beta of the securities A.Farber Vietnam 2004

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