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Intermediate
Alpha is a measure of risk-adjusted performance for individual securities or portfolios relative to a benchmark. It is derived from a regression of returns as the y-variable versus the benchmark as the x-variable. The intercept, where the line crosses the y-axis is the alpha measure. Normally used to evaluate an active portfolio manager, a positive alpha, over long periods such as 3 years, implies positive historical risk-adjusted performance.
Synonym: intercept, constant
Ken: Help me on the regression again. So
a manager with positive
alpha of say 1% is a good
manager.
Ann: Actually Ken, it just means they 'were'
a good manager over that time period.
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Alpha definition for investment modeling (3:53)
The script includes two sections where we visualize and demonstrate the calculation of alpha.
We're sitting right here in Excel, and this is a snippet from our boot camp course.
Here we plotted 60 monthly returns on the stock Merck on the y-axis. And 60 monthly returns on the Market plotted on the x-axis for the same time period.
So for this one month, the Market was up 10% and Merck was up 14%.
This line of best fit minimizes the difference between the line and each of the points. That's what linear regression does.
The intercept, or constant, or where the line crosses the y-axis, also in the formula here, is -0.0074%. That is alpha. And the formula for the line, given in y = mx + b format, reads like this: the historical monthly returns for Merck, were best described by a line where you would multiply the Market return by 1.2274 and then subtract 0.0074.
Again, alpha is a measure of risk-adjusted return. So relative to its market-related risk, Merck generated an alpha of -0.0074% per month.
Some people confuse alpha with the term active return, which would simply be subtracting the Market return from the Merck reutrn, and that wouldn't take risk into consideration. Next, let's demonstrate.
There are four ways to generate regression statistics in Excel.
First, you can use the chart output, but that isn't convenient.
A lot of people use the Data Analysis method, with output like this and alpha is down here described as Intercept.
Third is the function method, where you use the function called
=INTERCEPT()
. Input the stream of
returns for the y-variable first, then comma, then the x-variable
and hit Enter.
Fourth is the =LINEST()
method which
gives added functionality but is too advanced to cover here.
Click box for answer.
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