Area Under the Curve - Variable and Log Transformed Variable












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I have a situation where I am fitting two simple logistic regression models - one model with the variable of interest included as the only predictor, and the other model with the log of the variable of interest included as the only predictor. Both models have the same Area Under the Curve, and I would like to know how to explain why this occurs. I am sure this is not due to chance, but rather has something to do with how AUC is calculated, and it's interpretation.










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    $begingroup$


    I have a situation where I am fitting two simple logistic regression models - one model with the variable of interest included as the only predictor, and the other model with the log of the variable of interest included as the only predictor. Both models have the same Area Under the Curve, and I would like to know how to explain why this occurs. I am sure this is not due to chance, but rather has something to do with how AUC is calculated, and it's interpretation.










    share|cite|improve this question











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      2












      2








      2





      $begingroup$


      I have a situation where I am fitting two simple logistic regression models - one model with the variable of interest included as the only predictor, and the other model with the log of the variable of interest included as the only predictor. Both models have the same Area Under the Curve, and I would like to know how to explain why this occurs. I am sure this is not due to chance, but rather has something to do with how AUC is calculated, and it's interpretation.










      share|cite|improve this question











      $endgroup$




      I have a situation where I am fitting two simple logistic regression models - one model with the variable of interest included as the only predictor, and the other model with the log of the variable of interest included as the only predictor. Both models have the same Area Under the Curve, and I would like to know how to explain why this occurs. I am sure this is not due to chance, but rather has something to do with how AUC is calculated, and it's interpretation.







      logistic roc auc






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      edited 6 hours ago







      APK

















      asked 7 hours ago









      APKAPK

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      1278






















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          It is because the AUC is invariant to monotonic changes of variable, of which the log-transform is a special case. The AUC is the probability that a randomly selected case has a higher risk than a control. While the raw difference in risk may not be the same for those two models, the case will still have a higher risk when calculated using either the log-transformed predictor or the untransformed predictor.



          It should give us some pause and doubt about AUC that it makes no use whatsoever of the actual risk predicted by the model, but rather the ordering of groups according to a predicted risk (be it arbitrary or otherwise). The axes on a ROC are just sensitivity and 1-specificity.






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          • $begingroup$
            Thanks AdamO. Great explanation.
            $endgroup$
            – APK
            6 hours ago











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          1 Answer
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          1 Answer
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          $begingroup$

          It is because the AUC is invariant to monotonic changes of variable, of which the log-transform is a special case. The AUC is the probability that a randomly selected case has a higher risk than a control. While the raw difference in risk may not be the same for those two models, the case will still have a higher risk when calculated using either the log-transformed predictor or the untransformed predictor.



          It should give us some pause and doubt about AUC that it makes no use whatsoever of the actual risk predicted by the model, but rather the ordering of groups according to a predicted risk (be it arbitrary or otherwise). The axes on a ROC are just sensitivity and 1-specificity.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Thanks AdamO. Great explanation.
            $endgroup$
            – APK
            6 hours ago
















          3












          $begingroup$

          It is because the AUC is invariant to monotonic changes of variable, of which the log-transform is a special case. The AUC is the probability that a randomly selected case has a higher risk than a control. While the raw difference in risk may not be the same for those two models, the case will still have a higher risk when calculated using either the log-transformed predictor or the untransformed predictor.



          It should give us some pause and doubt about AUC that it makes no use whatsoever of the actual risk predicted by the model, but rather the ordering of groups according to a predicted risk (be it arbitrary or otherwise). The axes on a ROC are just sensitivity and 1-specificity.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Thanks AdamO. Great explanation.
            $endgroup$
            – APK
            6 hours ago














          3












          3








          3





          $begingroup$

          It is because the AUC is invariant to monotonic changes of variable, of which the log-transform is a special case. The AUC is the probability that a randomly selected case has a higher risk than a control. While the raw difference in risk may not be the same for those two models, the case will still have a higher risk when calculated using either the log-transformed predictor or the untransformed predictor.



          It should give us some pause and doubt about AUC that it makes no use whatsoever of the actual risk predicted by the model, but rather the ordering of groups according to a predicted risk (be it arbitrary or otherwise). The axes on a ROC are just sensitivity and 1-specificity.






          share|cite|improve this answer









          $endgroup$



          It is because the AUC is invariant to monotonic changes of variable, of which the log-transform is a special case. The AUC is the probability that a randomly selected case has a higher risk than a control. While the raw difference in risk may not be the same for those two models, the case will still have a higher risk when calculated using either the log-transformed predictor or the untransformed predictor.



          It should give us some pause and doubt about AUC that it makes no use whatsoever of the actual risk predicted by the model, but rather the ordering of groups according to a predicted risk (be it arbitrary or otherwise). The axes on a ROC are just sensitivity and 1-specificity.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered 7 hours ago









          AdamOAdamO

          33.8k263140




          33.8k263140












          • $begingroup$
            Thanks AdamO. Great explanation.
            $endgroup$
            – APK
            6 hours ago


















          • $begingroup$
            Thanks AdamO. Great explanation.
            $endgroup$
            – APK
            6 hours ago
















          $begingroup$
          Thanks AdamO. Great explanation.
          $endgroup$
          – APK
          6 hours ago




          $begingroup$
          Thanks AdamO. Great explanation.
          $endgroup$
          – APK
          6 hours ago


















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