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Thread: Cox PH model vs KM curves

  1. #1
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    Cox PH model vs KM curves

    Hello, everyone!

    I applied Cox PH model to my data and the results I got was quite reasonable. But I am a bit confused because it seems that conclusions for one particular predictor does not coincide between the Cox model and Kaplan-Meier group-specific survival curve estimation.

    In R i get :
    coef exp(coef) se(coef) z p
    chanell1 -0.12085 0.886 0.04532 -2.666 7.7e-03
    (i have not included coefficient estimates for other predictors in model)

    It seems that there is significant difference between hazards of the to chanells (1,2).

    But when looking at the corresponding KM survival curve (see attachment), it looks that they are almost equal. They even cross each other at some moment. So I think Cox model should not give significant coefficient for chanell1.

    What could be the explanation of this?
    Attached Images  

  2. #2
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    Re: Cox PH model vs KM curves

    I was just searching on the differences between KM and Cox model, one of the answers I found elsewhere is that Cox has a higher liability for Bias analyzing multiple predictors.
    I do not know further to this, sorry

  3. #3
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    Re: Cox PH model vs KM curves

    The KM results do not adjust for anything, while the Cox results do. You could try looking at the KM curve by stratifying by some other significant predictor that you've seen.

    For example if age is the most significant predictor, you could look at the KM curve for old subjects, and for young subjects.
    All things are known because we want to believe in them.

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