# CAPM - Equilibrium Theory

Discussion in 'P2.T8. Investment Management (15%)' started by dennis_cmpe, Oct 26, 2008.

Tags:
1. ### dennis_cmpeNew Member

In the study notes for CAPM Equilibrium Theory:

1) All assets must be held in portfolios, including the risky asset portfolio.

Sounds simple, but I'm not getting the importance of it. What does this mean? Why is this important?

2. ### David Harper CFA FRMDavid Harper CFA FRM (test)Staff Member

Dennis,

The theoretical significance is that is paves the way for the capital market line (CML). It is an implication (not a premise of) the assumptions underyling the CAPM (assigned Chapter 4, Noel Amenc). If you consider the CAPM assumptions--they are really unrealistic so it is just setting up they theory--a key idea is that all investors have the exact same information about the same set of assets and they also use the same risk/return perspective. In short, the investors are clones of each other therefore they must reach the same conclusion. This homogeneity ensures inclusion of all risky assets: if a stock is avoided, then all will avoid it, and it's price goes to zero. But it is very attractive at zero, so in unison, the investor will like it even at some low price. I can't say i personally find this implication of equilibrium particularly important, but it's on the way to the more important CAPM idea that a security's return/risk owe not to its individual characteristics (e.g., standard deviation) but rather its risk contribution (i.e., beta) to the market portfolio.

David

3. ### saurabhpal49New MemberSubscriber

Hi david,
I have some doubts regarding CAPM
>In capm there is homogenous expection, so why would some one be willing to sell market portfolio as all
investors want market portfolio?

>Could you please explain the below paragraph:
"The expected payoff of any asset remains constant under CAPM assumptions, such that when its price falls, its expected return increases. So, the expected return is at a point where supply is equal to demand in equilibrium"

>E(Rm)-Rf= risk aversion *6^2m

Why does increase in risk aversion increase the risk premium,
It should decreases as investor is unwilling to take more risk

Thanks

Last edited: Oct 26, 2017
4. ### David Harper CFA FRMDavid Harper CFA FRM (test)Staff Member

Hi @saurabhpal49 There is a lot of theory underlying CAPM (although I've trained it for years, I can't pretend to be a deep expert, I am more like a shallow expert; the Elton book is basically about CAPM theory).
• Homogenous expectations refers to the assumption that all market participants have the same view with respect to the limited inputs that matter in the restricted CAPM universe, which are: returns (or, equivalently prices), variances, and correlations. This is the meaning of "mean-variance:" they agree on means, variances and (related) the correlation (or, related, covariance) matrix. In my view, homogenous expectations leads all investors to the same optimal market portfolio (the portfolio of risky assets with the highest sharpe ratio). Ff you are interested, it so happens that literally yesterday I recorded/published a video to our youtube channel that is called "Capital market line (CML) versus security market line (SML), FRM T1-8" which includes a visualization of achieving the Market Portfolio (aka, mean-variance efficient portfolio, it is called by Ang) http://trtl.bz/2yPLQsa. My view is that, under the theory, homogeneous expectations leads all (equally-informed) investors to hold the same most-efficient Market Portfolio which itself is only the risky assets (the purple triangle in my video, snapshot below) such that, to your point, investors do not want to sell this portfolio. Rather, they are deciding only how to allocate between the Market Portfolio and the risk free asset (ie, where on the blue line will they locate?).
• Your second point is why investors would buy/sell individual securities. He is referring to (eg) the asset's future cash flow. If (eg) we all homogeneously agree that asset AA with a beta of 1.5 will pay future cash of $10.00 but its current price is$9.50, then it is currently priced too high b/c the expected return is only 10/9.50 - 1 = 5.3%. If the Rf rate = 3.0%, it will be sold until its price is down to \$8.93 because that is a price that is in equilibrium with its expected return of 12.0%. The idea is the current price adjusts according to an expected return, per PV = future cash/(1+ discount rate).