Why log-transform to normal distribution for decision trees?












1














On page 304 of chapter 8 of An Introduction to Statistical Learning with Applications in R (James et al.), the authors say:




We use the Hitters data set to predict a baseball player’s Salary based on Years (the number of years that he has played in the major leagues) and Hits (the number of hits that he made in the previous year). We first remove observations that are missing Salary values, and log-transform Salary so that its distribution has more of a typical bell-shape. (Recall that Salary is measured in thousands of dollars.)




No additional motivation for the log-transform is given. Being that the data are being fed into decision tree algorithms, why was it important to force the data into a normal distribution? I thought most/all decision tree algorithms were invariant to scale changes.










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    On page 304 of chapter 8 of An Introduction to Statistical Learning with Applications in R (James et al.), the authors say:




    We use the Hitters data set to predict a baseball player’s Salary based on Years (the number of years that he has played in the major leagues) and Hits (the number of hits that he made in the previous year). We first remove observations that are missing Salary values, and log-transform Salary so that its distribution has more of a typical bell-shape. (Recall that Salary is measured in thousands of dollars.)




    No additional motivation for the log-transform is given. Being that the data are being fed into decision tree algorithms, why was it important to force the data into a normal distribution? I thought most/all decision tree algorithms were invariant to scale changes.










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    New contributor




    jss367 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      1












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      1







      On page 304 of chapter 8 of An Introduction to Statistical Learning with Applications in R (James et al.), the authors say:




      We use the Hitters data set to predict a baseball player’s Salary based on Years (the number of years that he has played in the major leagues) and Hits (the number of hits that he made in the previous year). We first remove observations that are missing Salary values, and log-transform Salary so that its distribution has more of a typical bell-shape. (Recall that Salary is measured in thousands of dollars.)




      No additional motivation for the log-transform is given. Being that the data are being fed into decision tree algorithms, why was it important to force the data into a normal distribution? I thought most/all decision tree algorithms were invariant to scale changes.










      share|cite|improve this question









      New contributor




      jss367 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      On page 304 of chapter 8 of An Introduction to Statistical Learning with Applications in R (James et al.), the authors say:




      We use the Hitters data set to predict a baseball player’s Salary based on Years (the number of years that he has played in the major leagues) and Hits (the number of hits that he made in the previous year). We first remove observations that are missing Salary values, and log-transform Salary so that its distribution has more of a typical bell-shape. (Recall that Salary is measured in thousands of dollars.)




      No additional motivation for the log-transform is given. Being that the data are being fed into decision tree algorithms, why was it important to force the data into a normal distribution? I thought most/all decision tree algorithms were invariant to scale changes.







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      Sycorax

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          In this case, the salary is the target of the decision tree, not one of the features (independent variables/predictors). You are correct that decision trees are insensitive to the scale of the predictors, but since I suspect there are a small number of extremely large salaries, transforming the salaries might improve predictions because loss functions which minimize square error will not be so strongly influenced by these large values.






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            In this case, the salary is the target of the decision tree, not one of the features (independent variables/predictors). You are correct that decision trees are insensitive to the scale of the predictors, but since I suspect there are a small number of extremely large salaries, transforming the salaries might improve predictions because loss functions which minimize square error will not be so strongly influenced by these large values.






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              In this case, the salary is the target of the decision tree, not one of the features (independent variables/predictors). You are correct that decision trees are insensitive to the scale of the predictors, but since I suspect there are a small number of extremely large salaries, transforming the salaries might improve predictions because loss functions which minimize square error will not be so strongly influenced by these large values.






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                3






                In this case, the salary is the target of the decision tree, not one of the features (independent variables/predictors). You are correct that decision trees are insensitive to the scale of the predictors, but since I suspect there are a small number of extremely large salaries, transforming the salaries might improve predictions because loss functions which minimize square error will not be so strongly influenced by these large values.






                share|cite|improve this answer












                In this case, the salary is the target of the decision tree, not one of the features (independent variables/predictors). You are correct that decision trees are insensitive to the scale of the predictors, but since I suspect there are a small number of extremely large salaries, transforming the salaries might improve predictions because loss functions which minimize square error will not be so strongly influenced by these large values.







                share|cite|improve this answer












                share|cite|improve this answer



                share|cite|improve this answer










                answered 1 hour ago









                Sycorax

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