Why no variance term in Bayesian logistic regression?





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$begingroup$


I've read here that




... (Bayesian linear regression) is most similar to Bayesian inference
in logistic regression, but in some ways logistic regression is even
simpler, because there is no variance term to estimate, only the
regression parameters.




Why is it the case, why no variance term in Bayesian logistic regression?










share|cite|improve this question











$endgroup$



















    5












    $begingroup$


    I've read here that




    ... (Bayesian linear regression) is most similar to Bayesian inference
    in logistic regression, but in some ways logistic regression is even
    simpler, because there is no variance term to estimate, only the
    regression parameters.




    Why is it the case, why no variance term in Bayesian logistic regression?










    share|cite|improve this question











    $endgroup$















      5












      5








      5


      2



      $begingroup$


      I've read here that




      ... (Bayesian linear regression) is most similar to Bayesian inference
      in logistic regression, but in some ways logistic regression is even
      simpler, because there is no variance term to estimate, only the
      regression parameters.




      Why is it the case, why no variance term in Bayesian logistic regression?










      share|cite|improve this question











      $endgroup$




      I've read here that




      ... (Bayesian linear regression) is most similar to Bayesian inference
      in logistic regression, but in some ways logistic regression is even
      simpler, because there is no variance term to estimate, only the
      regression parameters.




      Why is it the case, why no variance term in Bayesian logistic regression?







      logistic bayesian generalized-linear-model variance bernoulli-distribution






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Apr 5 at 0:45









      Krantz

      36411




      36411










      asked Apr 3 at 20:32









      PatrickPatrick

      1596




      1596






















          1 Answer
          1






          active

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          votes


















          10












          $begingroup$

          Logistic regression, Bayesian or not, is a model defined in terms of Bernoulli distribution. The distribution is parametrized by "probability of success" $p$ with mean $p$ and variance $p(1-p)$, i.e. the variance directly follows from the mean. So there is no "separate" variance term, this is what the quote seems to say.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            @patrick for linear regression $y = mx + c + epsilon$, whereas logistic regression p(y=1|x) = logistic(mx +c).
            $endgroup$
            – seanv507
            Apr 3 at 21:02










          • $begingroup$
            @seanv507 and would it make sense to have $p(y=1|x)=logistic(mx+c+epsilon)$ or not? If not, is it because $p()$ is a probability and already includes some uncertainty?
            $endgroup$
            – Patrick
            Apr 3 at 21:37








          • 1




            $begingroup$
            @Patrick what would this formulation exactly mean? Could you give an example where would you imagine it to be used?
            $endgroup$
            – Tim
            Apr 3 at 21:39










          • $begingroup$
            @Patrick When you describe the conditional expectation in terms of a distribution there's no error term.
            $endgroup$
            – Firebug
            Apr 3 at 22:12






          • 1




            $begingroup$
            @Patrick linear regression is $Y sim mathcal{N}(Xbeta, sigma)$ while logistic regression is $Y sim mathcal{B}(h^{-1}(Xbeta))$. Error term is alternative way of writing linear regression, but in both cases you estimate mean of some distribution. So error term inside logistic regression would mean that you assume $h(p)$ to be normally distributed. This does not have to be nonsense, but I doubt that this is what you meant.
            $endgroup$
            – Tim
            Apr 4 at 19:12














          Your Answer





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          1 Answer
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          active

          oldest

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          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          10












          $begingroup$

          Logistic regression, Bayesian or not, is a model defined in terms of Bernoulli distribution. The distribution is parametrized by "probability of success" $p$ with mean $p$ and variance $p(1-p)$, i.e. the variance directly follows from the mean. So there is no "separate" variance term, this is what the quote seems to say.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            @patrick for linear regression $y = mx + c + epsilon$, whereas logistic regression p(y=1|x) = logistic(mx +c).
            $endgroup$
            – seanv507
            Apr 3 at 21:02










          • $begingroup$
            @seanv507 and would it make sense to have $p(y=1|x)=logistic(mx+c+epsilon)$ or not? If not, is it because $p()$ is a probability and already includes some uncertainty?
            $endgroup$
            – Patrick
            Apr 3 at 21:37








          • 1




            $begingroup$
            @Patrick what would this formulation exactly mean? Could you give an example where would you imagine it to be used?
            $endgroup$
            – Tim
            Apr 3 at 21:39










          • $begingroup$
            @Patrick When you describe the conditional expectation in terms of a distribution there's no error term.
            $endgroup$
            – Firebug
            Apr 3 at 22:12






          • 1




            $begingroup$
            @Patrick linear regression is $Y sim mathcal{N}(Xbeta, sigma)$ while logistic regression is $Y sim mathcal{B}(h^{-1}(Xbeta))$. Error term is alternative way of writing linear regression, but in both cases you estimate mean of some distribution. So error term inside logistic regression would mean that you assume $h(p)$ to be normally distributed. This does not have to be nonsense, but I doubt that this is what you meant.
            $endgroup$
            – Tim
            Apr 4 at 19:12


















          10












          $begingroup$

          Logistic regression, Bayesian or not, is a model defined in terms of Bernoulli distribution. The distribution is parametrized by "probability of success" $p$ with mean $p$ and variance $p(1-p)$, i.e. the variance directly follows from the mean. So there is no "separate" variance term, this is what the quote seems to say.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            @patrick for linear regression $y = mx + c + epsilon$, whereas logistic regression p(y=1|x) = logistic(mx +c).
            $endgroup$
            – seanv507
            Apr 3 at 21:02










          • $begingroup$
            @seanv507 and would it make sense to have $p(y=1|x)=logistic(mx+c+epsilon)$ or not? If not, is it because $p()$ is a probability and already includes some uncertainty?
            $endgroup$
            – Patrick
            Apr 3 at 21:37








          • 1




            $begingroup$
            @Patrick what would this formulation exactly mean? Could you give an example where would you imagine it to be used?
            $endgroup$
            – Tim
            Apr 3 at 21:39










          • $begingroup$
            @Patrick When you describe the conditional expectation in terms of a distribution there's no error term.
            $endgroup$
            – Firebug
            Apr 3 at 22:12






          • 1




            $begingroup$
            @Patrick linear regression is $Y sim mathcal{N}(Xbeta, sigma)$ while logistic regression is $Y sim mathcal{B}(h^{-1}(Xbeta))$. Error term is alternative way of writing linear regression, but in both cases you estimate mean of some distribution. So error term inside logistic regression would mean that you assume $h(p)$ to be normally distributed. This does not have to be nonsense, but I doubt that this is what you meant.
            $endgroup$
            – Tim
            Apr 4 at 19:12
















          10












          10








          10





          $begingroup$

          Logistic regression, Bayesian or not, is a model defined in terms of Bernoulli distribution. The distribution is parametrized by "probability of success" $p$ with mean $p$ and variance $p(1-p)$, i.e. the variance directly follows from the mean. So there is no "separate" variance term, this is what the quote seems to say.






          share|cite|improve this answer









          $endgroup$



          Logistic regression, Bayesian or not, is a model defined in terms of Bernoulli distribution. The distribution is parametrized by "probability of success" $p$ with mean $p$ and variance $p(1-p)$, i.e. the variance directly follows from the mean. So there is no "separate" variance term, this is what the quote seems to say.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Apr 3 at 20:46









          TimTim

          60k9133228




          60k9133228












          • $begingroup$
            @patrick for linear regression $y = mx + c + epsilon$, whereas logistic regression p(y=1|x) = logistic(mx +c).
            $endgroup$
            – seanv507
            Apr 3 at 21:02










          • $begingroup$
            @seanv507 and would it make sense to have $p(y=1|x)=logistic(mx+c+epsilon)$ or not? If not, is it because $p()$ is a probability and already includes some uncertainty?
            $endgroup$
            – Patrick
            Apr 3 at 21:37








          • 1




            $begingroup$
            @Patrick what would this formulation exactly mean? Could you give an example where would you imagine it to be used?
            $endgroup$
            – Tim
            Apr 3 at 21:39










          • $begingroup$
            @Patrick When you describe the conditional expectation in terms of a distribution there's no error term.
            $endgroup$
            – Firebug
            Apr 3 at 22:12






          • 1




            $begingroup$
            @Patrick linear regression is $Y sim mathcal{N}(Xbeta, sigma)$ while logistic regression is $Y sim mathcal{B}(h^{-1}(Xbeta))$. Error term is alternative way of writing linear regression, but in both cases you estimate mean of some distribution. So error term inside logistic regression would mean that you assume $h(p)$ to be normally distributed. This does not have to be nonsense, but I doubt that this is what you meant.
            $endgroup$
            – Tim
            Apr 4 at 19:12




















          • $begingroup$
            @patrick for linear regression $y = mx + c + epsilon$, whereas logistic regression p(y=1|x) = logistic(mx +c).
            $endgroup$
            – seanv507
            Apr 3 at 21:02










          • $begingroup$
            @seanv507 and would it make sense to have $p(y=1|x)=logistic(mx+c+epsilon)$ or not? If not, is it because $p()$ is a probability and already includes some uncertainty?
            $endgroup$
            – Patrick
            Apr 3 at 21:37








          • 1




            $begingroup$
            @Patrick what would this formulation exactly mean? Could you give an example where would you imagine it to be used?
            $endgroup$
            – Tim
            Apr 3 at 21:39










          • $begingroup$
            @Patrick When you describe the conditional expectation in terms of a distribution there's no error term.
            $endgroup$
            – Firebug
            Apr 3 at 22:12






          • 1




            $begingroup$
            @Patrick linear regression is $Y sim mathcal{N}(Xbeta, sigma)$ while logistic regression is $Y sim mathcal{B}(h^{-1}(Xbeta))$. Error term is alternative way of writing linear regression, but in both cases you estimate mean of some distribution. So error term inside logistic regression would mean that you assume $h(p)$ to be normally distributed. This does not have to be nonsense, but I doubt that this is what you meant.
            $endgroup$
            – Tim
            Apr 4 at 19:12


















          $begingroup$
          @patrick for linear regression $y = mx + c + epsilon$, whereas logistic regression p(y=1|x) = logistic(mx +c).
          $endgroup$
          – seanv507
          Apr 3 at 21:02




          $begingroup$
          @patrick for linear regression $y = mx + c + epsilon$, whereas logistic regression p(y=1|x) = logistic(mx +c).
          $endgroup$
          – seanv507
          Apr 3 at 21:02












          $begingroup$
          @seanv507 and would it make sense to have $p(y=1|x)=logistic(mx+c+epsilon)$ or not? If not, is it because $p()$ is a probability and already includes some uncertainty?
          $endgroup$
          – Patrick
          Apr 3 at 21:37






          $begingroup$
          @seanv507 and would it make sense to have $p(y=1|x)=logistic(mx+c+epsilon)$ or not? If not, is it because $p()$ is a probability and already includes some uncertainty?
          $endgroup$
          – Patrick
          Apr 3 at 21:37






          1




          1




          $begingroup$
          @Patrick what would this formulation exactly mean? Could you give an example where would you imagine it to be used?
          $endgroup$
          – Tim
          Apr 3 at 21:39




          $begingroup$
          @Patrick what would this formulation exactly mean? Could you give an example where would you imagine it to be used?
          $endgroup$
          – Tim
          Apr 3 at 21:39












          $begingroup$
          @Patrick When you describe the conditional expectation in terms of a distribution there's no error term.
          $endgroup$
          – Firebug
          Apr 3 at 22:12




          $begingroup$
          @Patrick When you describe the conditional expectation in terms of a distribution there's no error term.
          $endgroup$
          – Firebug
          Apr 3 at 22:12




          1




          1




          $begingroup$
          @Patrick linear regression is $Y sim mathcal{N}(Xbeta, sigma)$ while logistic regression is $Y sim mathcal{B}(h^{-1}(Xbeta))$. Error term is alternative way of writing linear regression, but in both cases you estimate mean of some distribution. So error term inside logistic regression would mean that you assume $h(p)$ to be normally distributed. This does not have to be nonsense, but I doubt that this is what you meant.
          $endgroup$
          – Tim
          Apr 4 at 19:12






          $begingroup$
          @Patrick linear regression is $Y sim mathcal{N}(Xbeta, sigma)$ while logistic regression is $Y sim mathcal{B}(h^{-1}(Xbeta))$. Error term is alternative way of writing linear regression, but in both cases you estimate mean of some distribution. So error term inside logistic regression would mean that you assume $h(p)$ to be normally distributed. This does not have to be nonsense, but I doubt that this is what you meant.
          $endgroup$
          – Tim
          Apr 4 at 19:12




















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