What you will learn
- Distinguish beta (market exposure) from alpha (skill)
- Compute alpha as the return beyond what CAPM predicts
- Understand why beta is cheap and alpha is scarce
- Judge performance honestly, separating luck from skill
Alpha and beta are two of the most used words in investing, and they come straight from the CAPM you just learned. Together they split any investment's performance into two very different sources: the return you got simply by being exposed to the market, and the return you got from genuine skill or edge. Telling them apart is one of the more useful things an investor can do.
What is beta? (MoneyWeek)
A practical explanation of beta as an investment's sensitivity to the market. This is the market-exposure half of performance.
Beta: market exposure you can buy cheaply
Beta, from the CAPM, measures how much of an investment's movement comes from riding the overall market. A beta of 1 moves with the market, above 1 amplifies it, below 1 dampens it, and a negative beta moves opposite it. The practical fact is that beta is cheap. Anyone can capture the market's return, its beta, for almost nothing by buying a low-cost index fund. You should never pay high fees for beta, because it is a commodity available to everyone.
Alpha: the return beyond the market
Alpha is the return an investment earns beyond what its beta would predict. From the last lesson, it is how far the investment sits above or below the security market line.
- actual return = what the investment earned
- CAPM expected return = what its beta warranted
A positive alpha means the investment did better than its market risk warranted, the signature of genuine skill or edge. A negative alpha means it did worse. Alpha is what active managers are really selling, and it is the rare and valuable thing that beta is not.
Key terms
- Beta
- The part of return that comes from market exposure. Cheap and available through index funds.
- Alpha
- The return beyond what beta predicts: actual return minus CAPM expected return. The mark of skill.
- Risk-adjusted evaluation
- Judging performance by return relative to the risk taken, not by raw return alone.
Computing alpha
A fund returned 12 percent last year. Given its beta, the CAPM said it should have been expected to return 9 percent. What was its alpha?
- Write the formula. Alpha is the actual return minus the CAPM expected return.
- Subtract. 12 percent minus 9 percent.
- Read the result. The alpha is positive 3 percent.
Why it matters: The fund beat what its market risk warranted by 3 percentage points. That gap is the value it added beyond simply riding the market, at least for this one year.
Compute an alpha
A fund returned 7 percent. The CAPM predicted an expected return of 8.4 percent for its level of market risk. What was its alpha, in percent? (A negative answer is possible.)
Why the distinction matters
Separating alpha from beta protects you from a very common trap. Suppose a manager posts a big return in a rising market. Did they generate real alpha through skill, or did they just crank up their beta, taking more market risk and getting carried up by the tide? These are completely different. A manager who merely loaded up on beta produced nothing you could not have gotten cheaply from an index fund, yet may charge high fees as if the return reflected skill. Always ask whether a strong return came from alpha or from simply dialing up market exposure.
Beta you can buy for pennies. Alpha is the rare, expensive thing, and much of what is sold as alpha is really beta in disguise, or luck in a nice suit.
What is alpha? (MoneyWeek)
The skill half of the picture: return beyond the market. Watch for why genuine alpha is so hard to find.
Alpha is hard to find and harder to keep
Here is the humbling part, and it leans on the statistics of Unit 5. Genuine, persistent alpha is very rare. Much of what looks like alpha turns out to be luck, hidden risk that has not shown up yet, or exposure to cheap factors dressed up as skill. After fees, the majority of active managers fail to beat a simple index over the long run. And a few years of outperformance prove little, because with thousands of managers, some will beat the market by chance alone, exactly the multiple-testing problem from Unit 5. Distinguishing real skill from a lucky streak takes many years of data and hard statistical scrutiny.
Skill or just beta?
In a year when the market rose 20 percent, a manager's fund rose 25 percent. The fund has a beta of 1.3. Should you conclude the manager has real skill?
A beta of 1.3 means the fund tends to amplify market moves, so in a 20 percent market you would expect a large gain from beta alone. Much or all of the 25 percent may be market exposure rather than alpha, so one strong year does not prove skill.Beta cheap, alpha scarce
In your own words, explain why an investor should pay very little for beta but demand strong evidence before paying for claimed alpha.
Write an answer before comparing it with the model response.
Model answer
Beta is just exposure to the overall market, and anyone can get it for almost nothing by buying a low-cost index fund, so it is a commodity not worth high fees. Alpha is return beyond what market exposure explains, the product of genuine skill, and it is rare, competitive, and easily faked by taking hidden risk or by getting lucky. Because a manager can dress up extra beta or a lucky streak as alpha, an investor should pay little for the market exposure they could buy cheaply and insist on long, statistically convincing evidence before paying premium fees for supposed skill.
Alpha and beta tell you where a return came from. But to compare investments with different risk levels fairly, you need a single risk-adjusted score. The next lesson builds it: the Sharpe ratio.