Exponential Distribution - ML estimator of λ in τ parametrization
I am stuck with the following problem: We know that $x_1 cdots x_n$ ~ Ex$(1/lambda)$ and we are given the sum $sum_{i=1}^n x_i$. We want to find the maximum likelihood estimate of $lambda$, as well as its variance. Also we want to find a $(1-alpha)$ - confidence interval.
I know that E $ [x_i] = 1/lambda $ and that the likelihood is $L(frac{1}{lambda} | x_1cdots x_n) = lambda^n e^{-sum_i x_ilambda}$. Therefore the ML estimate should be
begin{align}
hat{lambda}= frac{n}{sum_i x_i}.
end{align}
However, I don't know how to calculate the expectation value or the variance of $hat{lambda}$ as this involes $E[frac{1}{sum_i x_i}]$ and I know that normally
begin{align}
E [frac{1}{X}] > frac{1}{E[X]}.
end{align}
Therefore I guess that E$[hat{lambda}] > lambda$, but I don't know how I would calculate it. Thank you already.
statistics exponential-distribution
add a comment |
I am stuck with the following problem: We know that $x_1 cdots x_n$ ~ Ex$(1/lambda)$ and we are given the sum $sum_{i=1}^n x_i$. We want to find the maximum likelihood estimate of $lambda$, as well as its variance. Also we want to find a $(1-alpha)$ - confidence interval.
I know that E $ [x_i] = 1/lambda $ and that the likelihood is $L(frac{1}{lambda} | x_1cdots x_n) = lambda^n e^{-sum_i x_ilambda}$. Therefore the ML estimate should be
begin{align}
hat{lambda}= frac{n}{sum_i x_i}.
end{align}
However, I don't know how to calculate the expectation value or the variance of $hat{lambda}$ as this involes $E[frac{1}{sum_i x_i}]$ and I know that normally
begin{align}
E [frac{1}{X}] > frac{1}{E[X]}.
end{align}
Therefore I guess that E$[hat{lambda}] > lambda$, but I don't know how I would calculate it. Thank you already.
statistics exponential-distribution
$sum X_i sim Gamma(n,1/lambda)$, then find its variance.
– John_Wick
Nov 22 at 20:51
So var $[sum X_i ] = n/lambda^2$ ? I still don't see how this would help me as var $[1/X] neq 1/$var$[X]$, right?
– F. Moe
Nov 22 at 21:04
If $X$ is a random variable with support $Omega$ and pdf $f_X$, then $E(1/X)=int_Omega big(frac{1}{t}big)f_X(t)dt$, so like was mentioned use $Xsim Gamma(n,1/lambda)$
– gd1035
Nov 22 at 22:04
add a comment |
I am stuck with the following problem: We know that $x_1 cdots x_n$ ~ Ex$(1/lambda)$ and we are given the sum $sum_{i=1}^n x_i$. We want to find the maximum likelihood estimate of $lambda$, as well as its variance. Also we want to find a $(1-alpha)$ - confidence interval.
I know that E $ [x_i] = 1/lambda $ and that the likelihood is $L(frac{1}{lambda} | x_1cdots x_n) = lambda^n e^{-sum_i x_ilambda}$. Therefore the ML estimate should be
begin{align}
hat{lambda}= frac{n}{sum_i x_i}.
end{align}
However, I don't know how to calculate the expectation value or the variance of $hat{lambda}$ as this involes $E[frac{1}{sum_i x_i}]$ and I know that normally
begin{align}
E [frac{1}{X}] > frac{1}{E[X]}.
end{align}
Therefore I guess that E$[hat{lambda}] > lambda$, but I don't know how I would calculate it. Thank you already.
statistics exponential-distribution
I am stuck with the following problem: We know that $x_1 cdots x_n$ ~ Ex$(1/lambda)$ and we are given the sum $sum_{i=1}^n x_i$. We want to find the maximum likelihood estimate of $lambda$, as well as its variance. Also we want to find a $(1-alpha)$ - confidence interval.
I know that E $ [x_i] = 1/lambda $ and that the likelihood is $L(frac{1}{lambda} | x_1cdots x_n) = lambda^n e^{-sum_i x_ilambda}$. Therefore the ML estimate should be
begin{align}
hat{lambda}= frac{n}{sum_i x_i}.
end{align}
However, I don't know how to calculate the expectation value or the variance of $hat{lambda}$ as this involes $E[frac{1}{sum_i x_i}]$ and I know that normally
begin{align}
E [frac{1}{X}] > frac{1}{E[X]}.
end{align}
Therefore I guess that E$[hat{lambda}] > lambda$, but I don't know how I would calculate it. Thank you already.
statistics exponential-distribution
statistics exponential-distribution
asked Nov 22 at 20:47
F. Moe
205
205
$sum X_i sim Gamma(n,1/lambda)$, then find its variance.
– John_Wick
Nov 22 at 20:51
So var $[sum X_i ] = n/lambda^2$ ? I still don't see how this would help me as var $[1/X] neq 1/$var$[X]$, right?
– F. Moe
Nov 22 at 21:04
If $X$ is a random variable with support $Omega$ and pdf $f_X$, then $E(1/X)=int_Omega big(frac{1}{t}big)f_X(t)dt$, so like was mentioned use $Xsim Gamma(n,1/lambda)$
– gd1035
Nov 22 at 22:04
add a comment |
$sum X_i sim Gamma(n,1/lambda)$, then find its variance.
– John_Wick
Nov 22 at 20:51
So var $[sum X_i ] = n/lambda^2$ ? I still don't see how this would help me as var $[1/X] neq 1/$var$[X]$, right?
– F. Moe
Nov 22 at 21:04
If $X$ is a random variable with support $Omega$ and pdf $f_X$, then $E(1/X)=int_Omega big(frac{1}{t}big)f_X(t)dt$, so like was mentioned use $Xsim Gamma(n,1/lambda)$
– gd1035
Nov 22 at 22:04
$sum X_i sim Gamma(n,1/lambda)$, then find its variance.
– John_Wick
Nov 22 at 20:51
$sum X_i sim Gamma(n,1/lambda)$, then find its variance.
– John_Wick
Nov 22 at 20:51
So var $[sum X_i ] = n/lambda^2$ ? I still don't see how this would help me as var $[1/X] neq 1/$var$[X]$, right?
– F. Moe
Nov 22 at 21:04
So var $[sum X_i ] = n/lambda^2$ ? I still don't see how this would help me as var $[1/X] neq 1/$var$[X]$, right?
– F. Moe
Nov 22 at 21:04
If $X$ is a random variable with support $Omega$ and pdf $f_X$, then $E(1/X)=int_Omega big(frac{1}{t}big)f_X(t)dt$, so like was mentioned use $Xsim Gamma(n,1/lambda)$
– gd1035
Nov 22 at 22:04
If $X$ is a random variable with support $Omega$ and pdf $f_X$, then $E(1/X)=int_Omega big(frac{1}{t}big)f_X(t)dt$, so like was mentioned use $Xsim Gamma(n,1/lambda)$
– gd1035
Nov 22 at 22:04
add a comment |
1 Answer
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$S=sum X_i sim Gamma(n, 1/lambda).$ If $Ssim Gamma(n,a)$ then $E(S^t)=int_0^infty x^t frac{1}{Gamma(n)a^n}e^{-x/a}x^{n-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}int_0^infty frac{1}{Gamma(n+t)a^{n+t}}e^{-x/a}x^{n+t-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}$ for all $t>-n$.
$Var(n/S)=E(n^2/S^2)-E^2(n/S)=n^2left(frac{Gamma(n-2)a^{n-2}}{Gamma(n)a^n}-left(frac{Gamma(n-1)a^{n-1}}{Gamma(n)a^n}right)^2right)=n^2left(frac{1}{(n-1)(n-2)a^2}-left(frac{1}{(n-1)a}right)^2right)=frac{n^2}{a^2(n-1)^2(n-2)}.$
Thank you for clarifying! In your calculation of $E(S^t)$ you forgot the $a$ in the exponent, right? So it would be $e^{-x/a}$. Am I right that $E(hat{lambda})$ then is $E(hat{lambda}) = n frac{Gamma(n-1)}{Gamma(n)} lambda$?
– F. Moe
Nov 22 at 22:53
Yes, that is correct.
– John_Wick
Nov 22 at 22:55
Great! Just one more question: will the confidence interval for $lambda$ be just taken from the regular Gamma quantiles, i.e. from Gamma$(1,frac{1}{lambda})$ as Ex$(frac{1}{lambda}) = $Gamma$(1,frac{1}{lambda})$ ?
– F. Moe
Nov 22 at 23:08
Yes, you can find the bounds for CI using quantiles for Gamma.
– John_Wick
Nov 22 at 23:10
Thanks again. You really helped me clarify all this in my mind!
– F. Moe
Nov 22 at 23:12
add a comment |
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$S=sum X_i sim Gamma(n, 1/lambda).$ If $Ssim Gamma(n,a)$ then $E(S^t)=int_0^infty x^t frac{1}{Gamma(n)a^n}e^{-x/a}x^{n-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}int_0^infty frac{1}{Gamma(n+t)a^{n+t}}e^{-x/a}x^{n+t-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}$ for all $t>-n$.
$Var(n/S)=E(n^2/S^2)-E^2(n/S)=n^2left(frac{Gamma(n-2)a^{n-2}}{Gamma(n)a^n}-left(frac{Gamma(n-1)a^{n-1}}{Gamma(n)a^n}right)^2right)=n^2left(frac{1}{(n-1)(n-2)a^2}-left(frac{1}{(n-1)a}right)^2right)=frac{n^2}{a^2(n-1)^2(n-2)}.$
Thank you for clarifying! In your calculation of $E(S^t)$ you forgot the $a$ in the exponent, right? So it would be $e^{-x/a}$. Am I right that $E(hat{lambda})$ then is $E(hat{lambda}) = n frac{Gamma(n-1)}{Gamma(n)} lambda$?
– F. Moe
Nov 22 at 22:53
Yes, that is correct.
– John_Wick
Nov 22 at 22:55
Great! Just one more question: will the confidence interval for $lambda$ be just taken from the regular Gamma quantiles, i.e. from Gamma$(1,frac{1}{lambda})$ as Ex$(frac{1}{lambda}) = $Gamma$(1,frac{1}{lambda})$ ?
– F. Moe
Nov 22 at 23:08
Yes, you can find the bounds for CI using quantiles for Gamma.
– John_Wick
Nov 22 at 23:10
Thanks again. You really helped me clarify all this in my mind!
– F. Moe
Nov 22 at 23:12
add a comment |
$S=sum X_i sim Gamma(n, 1/lambda).$ If $Ssim Gamma(n,a)$ then $E(S^t)=int_0^infty x^t frac{1}{Gamma(n)a^n}e^{-x/a}x^{n-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}int_0^infty frac{1}{Gamma(n+t)a^{n+t}}e^{-x/a}x^{n+t-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}$ for all $t>-n$.
$Var(n/S)=E(n^2/S^2)-E^2(n/S)=n^2left(frac{Gamma(n-2)a^{n-2}}{Gamma(n)a^n}-left(frac{Gamma(n-1)a^{n-1}}{Gamma(n)a^n}right)^2right)=n^2left(frac{1}{(n-1)(n-2)a^2}-left(frac{1}{(n-1)a}right)^2right)=frac{n^2}{a^2(n-1)^2(n-2)}.$
Thank you for clarifying! In your calculation of $E(S^t)$ you forgot the $a$ in the exponent, right? So it would be $e^{-x/a}$. Am I right that $E(hat{lambda})$ then is $E(hat{lambda}) = n frac{Gamma(n-1)}{Gamma(n)} lambda$?
– F. Moe
Nov 22 at 22:53
Yes, that is correct.
– John_Wick
Nov 22 at 22:55
Great! Just one more question: will the confidence interval for $lambda$ be just taken from the regular Gamma quantiles, i.e. from Gamma$(1,frac{1}{lambda})$ as Ex$(frac{1}{lambda}) = $Gamma$(1,frac{1}{lambda})$ ?
– F. Moe
Nov 22 at 23:08
Yes, you can find the bounds for CI using quantiles for Gamma.
– John_Wick
Nov 22 at 23:10
Thanks again. You really helped me clarify all this in my mind!
– F. Moe
Nov 22 at 23:12
add a comment |
$S=sum X_i sim Gamma(n, 1/lambda).$ If $Ssim Gamma(n,a)$ then $E(S^t)=int_0^infty x^t frac{1}{Gamma(n)a^n}e^{-x/a}x^{n-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}int_0^infty frac{1}{Gamma(n+t)a^{n+t}}e^{-x/a}x^{n+t-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}$ for all $t>-n$.
$Var(n/S)=E(n^2/S^2)-E^2(n/S)=n^2left(frac{Gamma(n-2)a^{n-2}}{Gamma(n)a^n}-left(frac{Gamma(n-1)a^{n-1}}{Gamma(n)a^n}right)^2right)=n^2left(frac{1}{(n-1)(n-2)a^2}-left(frac{1}{(n-1)a}right)^2right)=frac{n^2}{a^2(n-1)^2(n-2)}.$
$S=sum X_i sim Gamma(n, 1/lambda).$ If $Ssim Gamma(n,a)$ then $E(S^t)=int_0^infty x^t frac{1}{Gamma(n)a^n}e^{-x/a}x^{n-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}int_0^infty frac{1}{Gamma(n+t)a^{n+t}}e^{-x/a}x^{n+t-1}dx=frac{Gamma(n+t)a^{n+t}}{Gamma(n)a^n}$ for all $t>-n$.
$Var(n/S)=E(n^2/S^2)-E^2(n/S)=n^2left(frac{Gamma(n-2)a^{n-2}}{Gamma(n)a^n}-left(frac{Gamma(n-1)a^{n-1}}{Gamma(n)a^n}right)^2right)=n^2left(frac{1}{(n-1)(n-2)a^2}-left(frac{1}{(n-1)a}right)^2right)=frac{n^2}{a^2(n-1)^2(n-2)}.$
edited Nov 22 at 22:56
answered Nov 22 at 21:19
John_Wick
1,346111
1,346111
Thank you for clarifying! In your calculation of $E(S^t)$ you forgot the $a$ in the exponent, right? So it would be $e^{-x/a}$. Am I right that $E(hat{lambda})$ then is $E(hat{lambda}) = n frac{Gamma(n-1)}{Gamma(n)} lambda$?
– F. Moe
Nov 22 at 22:53
Yes, that is correct.
– John_Wick
Nov 22 at 22:55
Great! Just one more question: will the confidence interval for $lambda$ be just taken from the regular Gamma quantiles, i.e. from Gamma$(1,frac{1}{lambda})$ as Ex$(frac{1}{lambda}) = $Gamma$(1,frac{1}{lambda})$ ?
– F. Moe
Nov 22 at 23:08
Yes, you can find the bounds for CI using quantiles for Gamma.
– John_Wick
Nov 22 at 23:10
Thanks again. You really helped me clarify all this in my mind!
– F. Moe
Nov 22 at 23:12
add a comment |
Thank you for clarifying! In your calculation of $E(S^t)$ you forgot the $a$ in the exponent, right? So it would be $e^{-x/a}$. Am I right that $E(hat{lambda})$ then is $E(hat{lambda}) = n frac{Gamma(n-1)}{Gamma(n)} lambda$?
– F. Moe
Nov 22 at 22:53
Yes, that is correct.
– John_Wick
Nov 22 at 22:55
Great! Just one more question: will the confidence interval for $lambda$ be just taken from the regular Gamma quantiles, i.e. from Gamma$(1,frac{1}{lambda})$ as Ex$(frac{1}{lambda}) = $Gamma$(1,frac{1}{lambda})$ ?
– F. Moe
Nov 22 at 23:08
Yes, you can find the bounds for CI using quantiles for Gamma.
– John_Wick
Nov 22 at 23:10
Thanks again. You really helped me clarify all this in my mind!
– F. Moe
Nov 22 at 23:12
Thank you for clarifying! In your calculation of $E(S^t)$ you forgot the $a$ in the exponent, right? So it would be $e^{-x/a}$. Am I right that $E(hat{lambda})$ then is $E(hat{lambda}) = n frac{Gamma(n-1)}{Gamma(n)} lambda$?
– F. Moe
Nov 22 at 22:53
Thank you for clarifying! In your calculation of $E(S^t)$ you forgot the $a$ in the exponent, right? So it would be $e^{-x/a}$. Am I right that $E(hat{lambda})$ then is $E(hat{lambda}) = n frac{Gamma(n-1)}{Gamma(n)} lambda$?
– F. Moe
Nov 22 at 22:53
Yes, that is correct.
– John_Wick
Nov 22 at 22:55
Yes, that is correct.
– John_Wick
Nov 22 at 22:55
Great! Just one more question: will the confidence interval for $lambda$ be just taken from the regular Gamma quantiles, i.e. from Gamma$(1,frac{1}{lambda})$ as Ex$(frac{1}{lambda}) = $Gamma$(1,frac{1}{lambda})$ ?
– F. Moe
Nov 22 at 23:08
Great! Just one more question: will the confidence interval for $lambda$ be just taken from the regular Gamma quantiles, i.e. from Gamma$(1,frac{1}{lambda})$ as Ex$(frac{1}{lambda}) = $Gamma$(1,frac{1}{lambda})$ ?
– F. Moe
Nov 22 at 23:08
Yes, you can find the bounds for CI using quantiles for Gamma.
– John_Wick
Nov 22 at 23:10
Yes, you can find the bounds for CI using quantiles for Gamma.
– John_Wick
Nov 22 at 23:10
Thanks again. You really helped me clarify all this in my mind!
– F. Moe
Nov 22 at 23:12
Thanks again. You really helped me clarify all this in my mind!
– F. Moe
Nov 22 at 23:12
add a comment |
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$sum X_i sim Gamma(n,1/lambda)$, then find its variance.
– John_Wick
Nov 22 at 20:51
So var $[sum X_i ] = n/lambda^2$ ? I still don't see how this would help me as var $[1/X] neq 1/$var$[X]$, right?
– F. Moe
Nov 22 at 21:04
If $X$ is a random variable with support $Omega$ and pdf $f_X$, then $E(1/X)=int_Omega big(frac{1}{t}big)f_X(t)dt$, so like was mentioned use $Xsim Gamma(n,1/lambda)$
– gd1035
Nov 22 at 22:04