R-Squared vs. Adjusted R-Squared: An Overview

R-squared and adjusted R-squared enable investors to measure the performance of a mutual fund against that of a benchmark. Investors may also use them to calculate the performance of their portfolio against a given benchmark.

In the world of investing, R-squared is expressed as a percentage between 0 and 100, with 100 signaling perfect correlation and zero no correlation at all. The figure does not indicate how well a particular group of securities is performing. It only measures how closely the returns align with those of the measured benchmark. It is also backwards-looking—it is not a predictor of future results.

Adjusted R-squared can provide a more precise view of that correlation by also taking into account how many independent variables are added to a particular model against which the stock index is measured. This is done because such additions of independent variables usually increase the reliability of that model—meaning, for investors, the correlation with the index.

Key Takeaways

  • R-squared and the adjusted R-squared both help investors measure the correlation between a mutual fund or portfolio with a stock index.
  • Adjusted R-squared, a modified version of R-squared, adds precision and reliability by considering the impact of additional independent variables that tend to skew the results of R-squared measurements.
  • The predicted R-squared, unlike the adjusted R-squared, is used to indicate how well a regression model predicts responses for new observations.
  • One misconception about regression analysis is that a low R-squared value is always a bad thing.

R-Squared

R-squared (R2) is a statistical measure that represents the proportion of the variance for a dependent variable that's explained by an independent variable or variables in a regression model. R-squared explains to what extent the variance of one variable explains the variance of the second variable. So, if the R2 of a model is 0.50, then approximately half of the observed variation can be explained by the model's inputs.

An R-squared result of 70 to 100 indicates that a given portfolio closely tracks the stock index in question, while a score between 0 and 40 indicates a very low correlation with the index. Higher R-squared values also indicate the reliability of beta readings. Beta measures the volatility of a security or a portfolio.

While R-squared can return a figure that indicates a level of correlation with an index, it has certain limitations when it comes to measuring the impact of independent variables on the correlation. This is where adjusted R-squared is useful in measuring correlation.

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Adjusted R-Squared

Adjusted R-squared is a modified version of R-squared that has been adjusted for the number of predictors in the model. The adjusted R-squared increases when the new term improves the model more than would be expected by chance. It decreases when a predictor improves the model by less than expected. Typically, the adjusted R-squared is positive, not negative. It is always lower than the R-squared.

Adding more independent variables or predictors to a regression model tends to increase the R-squared value, which tempts makers of the model to add even more variables. This is called overfitting and can return an unwarranted high R-squared value. Adjusted R-squared is used to determine how reliable the correlation is and how much it is determined by the addition of independent variables.

In a portfolio model that has more independent variables, adjusted R-squared will help determine how much of the correlation with the index is due to the addition of those variables. The adjusted R-squared compensates for the addition of variables and only increases if the new predictor enhances the model above what would be obtained by probability. Conversely, it will decrease when a predictor improves the model less than what is predicted by chance.

Key Differences

The most obvious difference between adjusted R-squared and R-squared is simply that adjusted R-squared considers and tests different independent variables against the stock index and R-squared does not. Because of this, many investment professionals prefer using adjusted R-squared because it has the potential to be more accurate. Furthermore, investors can gain additional information about what is affecting a stock by testing various independent variables using the adjusted R-squared model.

R-squared, on the other hand, does have its limitations. One of the most essential limits to using this model is that R-squared cannot be used to determine whether or not the coefficient estimates and predictions are biased. Furthermore,  in multiple linear regression, the R-squared can not tell us which regression variable is more important than the other.

Adjusted R-squared vs. Predicted R-Squared

The predicted R-squared, unlike the adjusted R-squared, is used to indicate how well a regression model predicts responses for new observations. So where the adjusted R-squared can provide an accurate model that fits the current data, the predicted R-squared determines how likely it is that this model will be accurate for future data.

R-Squared vs. Adjusted R-Squared Examples

When you are analyzing a situation in which there is a guarantee of little to no bias, using R-squared to calculate the relationship between two variables is perfectly useful. However, when investigating the relationship between say, the performance of a single stock and the rest of the S&P500, it is important to use adjusted R-squared to determine any inconsistencies in the correlation.

If an investor is looking for an index fund that closely tracks the S&P500, they will want to test different independent variables against the stock index such as the industry, the assets under management, how long the stock has been available on the market, and so on to ensure they have the most accurate figure of the correlation.

Special Considerations

R-Squared and Goodness-of-Fit

The basic idea of regression analysis is that if the deviations between the observed values and the predicted values of the linear model are small, the model has well-fit data. Goodness-of-fit is a mathematical model that helps to explain and account for the difference between this observed data and the predicted data. In other words, goodness-of-fit is a statistical hypothesis test to see how well sample data fit a distribution from a population with a normal distribution.

Low R-Squared vs. High R-Squared Value

One misconception about regression analysis is that a low R-squared value is always a bad thing. This is not so. For example, some data sets or fields of study have an inherently greater amount of unexplained variation. In this case, R-squared values are naturally going to be lower. Investigators can make useful conclusions about the data even with a low R-squared value.

In a different case, such as in investing, a high R-squared value—typically between 85% and 100%—indicates the stock or fund's performance moves relatively in line with the index. This is very useful information to investors thus a higher R-squared value is necessary for a successful project.

R-Squared vs. Adjusted R-Squared FAQs

What Is the Difference Between R-Squared and Adjusted R-Squared?

The most vital difference between adjusted R-squared and R-squared is simply that adjusted R-squared considers and tests different independent variables against the model and R-squared does not.

Which Is Better, R-Squared or Adjusted R-Squared?

Many investors prefer adjusted R-squared because adjusted R-squared can provide a more precise view of the correlation by also taking into account how many independent variables are added to a particular model against which the stock index is measured.

Should I Use Adjusted R-Squared or R-Squared?

Many investors have found success using adjusted R-squared over R-squared because of its ability to make a more accurate view of the correlation between one variable and another. Adjusted R-squared does this by taking into account how many independent variables are added to a particular model against which the stock index is measured.

What Is an Acceptable R-Squared Value?

Many people believe there is a magic number when it comes to determining an R-squared value that marks the sign of a valid study however this is not so. Because some data sets are inherently set up to have more unexpected variations than others, obtaining a high R-squared value is not always realistic. However, in certain cases an R-squared value between 70-90% is ideal.

The Bottom Line

R-squared and adjusted R-squared enable investors to measure the performance of a mutual fund against that of a benchmark. Many investors have found success using adjusted R-squared over R-squared because of its ability to make a more accurate view of the correlation between one variable and another.