$E(X^2)$ of discrete uniform distributionHow is Efron–Stein inequality usefulFor $X_i$ iid $ Var( sum_i=1^n X_i )= sum_i=1^n Var (X_i)$?Convergence in distribution from PGFCalculating variance of marginal distributionConsistent estimator of the meanHard time factoring Normal Distribution based on transformation problem.Expectation and Variance of a RatioDeriving which estimator is preferred for success probability $p$?Counting pairs of $k$-cycles with $r$ common edges (Variance of number of $k$-cycles)Higher Moments of a Cauchy Distribution
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$E(X^2)$ of discrete uniform distribution
How is Efron–Stein inequality usefulFor $X_i$ iid $ Var( sum_i=1^n X_i )= sum_i=1^n Var (X_i)$?Convergence in distribution from PGFCalculating variance of marginal distributionConsistent estimator of the meanHard time factoring Normal Distribution based on transformation problem.Expectation and Variance of a RatioDeriving which estimator is preferred for success probability $p$?Counting pairs of $k$-cycles with $r$ common edges (Variance of number of $k$-cycles)Higher Moments of a Cauchy Distribution
$begingroup$
I have a discrete uniform distribution (from IFoA formulae) with parameters a, b, h, where a and b are the start/end points, and h is the interval between each value. The p.d.f. is given as $frachb-a+h$. I manage to find out $$E[X] = sum_xin X xf(x) = sum_xin X fracxhb-a+h = frachb-a+hsum_xin X x\= frachb-a+htimes fraca+b2times fracb-a+hh = fraca+b2.$$ However, I cannot figure out the second moment ($E[X^2]$) and Variance by using the same method. I wonder if it is possible to find them using the same way, I know they could be found by using the M.G.F., I just want to know if it is possible.
$Var(X) = frac(b-a)(b-a+2h)12$ is given by the formulae.
Here is what I have got so far:
$$sum_xin X x^2f(x) = sum_xin X fracx^2 hb-a+h = frachb-a+hsum_xin X x^2=frachb-a+hsum_k=0^fracb-a+hh(hk+a)^2$$
edit:
beginalign*
E[X^2] &= sum_xin X x^2f(x)\
&=frach^3b-a+hsum_k=0^fracb-a+hhk^2+frac2ah^2b-a+hsum_k=0^fracb-a+hhk+fraca^2hb-a+hsum_k=0^fracb-a+hh1\
&=frach^3b-a+hfrac(fracb-ah)(fracb-ah+1)(2(fracb-ah)+1)6+frac2ah^2b-a+hfrac(fracb-ah+1)(fracb-ah)2+fraca^2hb-a+hbigg(fracb-ah+1bigg)\
&= frach^3b-a+hfrac(fracb-ah)(fracb-a+hh)(frac2(b-a)+hh)6+frac2ah^2b-a+hfrac(fracb-a+hh)(fracb-ah)2+fraca^2hb-a+hbigg(fracb-a+hhbigg)\
&= frac(b-a)(2(b-a)+h)6+a(b-a)+a^2\
Var(X) &= E[X^2] - E[X]^2\
&= frac(b-a)(2(b-a)+h)6+a(b-a)+a^2 - bigg(fraca+b2bigg)^2\
&= frac2(b-a)(2(b-a)+h)+12a(b-a)+12a^212 - frac3(a+b)^212\
&= frac4b^2-4ab+2bh-4ab+4a^2-2ah+12ab-12a^2+12a^2-3a^2-6ab-3b^212\
&= frac(a-b)^2+2h(b-a)12 \
&= frac(b-a)^2+2h(b-a)12\
&= frac(b-a)(b-a+2h)12
endalign*
probability uniform-distribution
$endgroup$
|
show 1 more comment
$begingroup$
I have a discrete uniform distribution (from IFoA formulae) with parameters a, b, h, where a and b are the start/end points, and h is the interval between each value. The p.d.f. is given as $frachb-a+h$. I manage to find out $$E[X] = sum_xin X xf(x) = sum_xin X fracxhb-a+h = frachb-a+hsum_xin X x\= frachb-a+htimes fraca+b2times fracb-a+hh = fraca+b2.$$ However, I cannot figure out the second moment ($E[X^2]$) and Variance by using the same method. I wonder if it is possible to find them using the same way, I know they could be found by using the M.G.F., I just want to know if it is possible.
$Var(X) = frac(b-a)(b-a+2h)12$ is given by the formulae.
Here is what I have got so far:
$$sum_xin X x^2f(x) = sum_xin X fracx^2 hb-a+h = frachb-a+hsum_xin X x^2=frachb-a+hsum_k=0^fracb-a+hh(hk+a)^2$$
edit:
beginalign*
E[X^2] &= sum_xin X x^2f(x)\
&=frach^3b-a+hsum_k=0^fracb-a+hhk^2+frac2ah^2b-a+hsum_k=0^fracb-a+hhk+fraca^2hb-a+hsum_k=0^fracb-a+hh1\
&=frach^3b-a+hfrac(fracb-ah)(fracb-ah+1)(2(fracb-ah)+1)6+frac2ah^2b-a+hfrac(fracb-ah+1)(fracb-ah)2+fraca^2hb-a+hbigg(fracb-ah+1bigg)\
&= frach^3b-a+hfrac(fracb-ah)(fracb-a+hh)(frac2(b-a)+hh)6+frac2ah^2b-a+hfrac(fracb-a+hh)(fracb-ah)2+fraca^2hb-a+hbigg(fracb-a+hhbigg)\
&= frac(b-a)(2(b-a)+h)6+a(b-a)+a^2\
Var(X) &= E[X^2] - E[X]^2\
&= frac(b-a)(2(b-a)+h)6+a(b-a)+a^2 - bigg(fraca+b2bigg)^2\
&= frac2(b-a)(2(b-a)+h)+12a(b-a)+12a^212 - frac3(a+b)^212\
&= frac4b^2-4ab+2bh-4ab+4a^2-2ah+12ab-12a^2+12a^2-3a^2-6ab-3b^212\
&= frac(a-b)^2+2h(b-a)12 \
&= frac(b-a)^2+2h(b-a)12\
&= frac(b-a)(b-a+2h)12
endalign*
probability uniform-distribution
$endgroup$
$begingroup$
Would it help if you knew that $sum_x=0^n x^2 = fracn(n+1)(2n+1)6$?
$endgroup$
– Paul
Oct 2 '18 at 14:33
$begingroup$
It would be helpful for $h = 1$, but I cannot imply it for $hneq1$.
$endgroup$
– VincentN
Oct 2 '18 at 14:36
$begingroup$
You can apply it for $x'=x/h$.
$endgroup$
– Paul
Oct 2 '18 at 14:38
$begingroup$
I don't quite get what you mean by that.
$endgroup$
– VincentN
Oct 2 '18 at 14:53
$begingroup$
I'll put it in an answer.
$endgroup$
– Paul
Oct 2 '18 at 14:57
|
show 1 more comment
$begingroup$
I have a discrete uniform distribution (from IFoA formulae) with parameters a, b, h, where a and b are the start/end points, and h is the interval between each value. The p.d.f. is given as $frachb-a+h$. I manage to find out $$E[X] = sum_xin X xf(x) = sum_xin X fracxhb-a+h = frachb-a+hsum_xin X x\= frachb-a+htimes fraca+b2times fracb-a+hh = fraca+b2.$$ However, I cannot figure out the second moment ($E[X^2]$) and Variance by using the same method. I wonder if it is possible to find them using the same way, I know they could be found by using the M.G.F., I just want to know if it is possible.
$Var(X) = frac(b-a)(b-a+2h)12$ is given by the formulae.
Here is what I have got so far:
$$sum_xin X x^2f(x) = sum_xin X fracx^2 hb-a+h = frachb-a+hsum_xin X x^2=frachb-a+hsum_k=0^fracb-a+hh(hk+a)^2$$
edit:
beginalign*
E[X^2] &= sum_xin X x^2f(x)\
&=frach^3b-a+hsum_k=0^fracb-a+hhk^2+frac2ah^2b-a+hsum_k=0^fracb-a+hhk+fraca^2hb-a+hsum_k=0^fracb-a+hh1\
&=frach^3b-a+hfrac(fracb-ah)(fracb-ah+1)(2(fracb-ah)+1)6+frac2ah^2b-a+hfrac(fracb-ah+1)(fracb-ah)2+fraca^2hb-a+hbigg(fracb-ah+1bigg)\
&= frach^3b-a+hfrac(fracb-ah)(fracb-a+hh)(frac2(b-a)+hh)6+frac2ah^2b-a+hfrac(fracb-a+hh)(fracb-ah)2+fraca^2hb-a+hbigg(fracb-a+hhbigg)\
&= frac(b-a)(2(b-a)+h)6+a(b-a)+a^2\
Var(X) &= E[X^2] - E[X]^2\
&= frac(b-a)(2(b-a)+h)6+a(b-a)+a^2 - bigg(fraca+b2bigg)^2\
&= frac2(b-a)(2(b-a)+h)+12a(b-a)+12a^212 - frac3(a+b)^212\
&= frac4b^2-4ab+2bh-4ab+4a^2-2ah+12ab-12a^2+12a^2-3a^2-6ab-3b^212\
&= frac(a-b)^2+2h(b-a)12 \
&= frac(b-a)^2+2h(b-a)12\
&= frac(b-a)(b-a+2h)12
endalign*
probability uniform-distribution
$endgroup$
I have a discrete uniform distribution (from IFoA formulae) with parameters a, b, h, where a and b are the start/end points, and h is the interval between each value. The p.d.f. is given as $frachb-a+h$. I manage to find out $$E[X] = sum_xin X xf(x) = sum_xin X fracxhb-a+h = frachb-a+hsum_xin X x\= frachb-a+htimes fraca+b2times fracb-a+hh = fraca+b2.$$ However, I cannot figure out the second moment ($E[X^2]$) and Variance by using the same method. I wonder if it is possible to find them using the same way, I know they could be found by using the M.G.F., I just want to know if it is possible.
$Var(X) = frac(b-a)(b-a+2h)12$ is given by the formulae.
Here is what I have got so far:
$$sum_xin X x^2f(x) = sum_xin X fracx^2 hb-a+h = frachb-a+hsum_xin X x^2=frachb-a+hsum_k=0^fracb-a+hh(hk+a)^2$$
edit:
beginalign*
E[X^2] &= sum_xin X x^2f(x)\
&=frach^3b-a+hsum_k=0^fracb-a+hhk^2+frac2ah^2b-a+hsum_k=0^fracb-a+hhk+fraca^2hb-a+hsum_k=0^fracb-a+hh1\
&=frach^3b-a+hfrac(fracb-ah)(fracb-ah+1)(2(fracb-ah)+1)6+frac2ah^2b-a+hfrac(fracb-ah+1)(fracb-ah)2+fraca^2hb-a+hbigg(fracb-ah+1bigg)\
&= frach^3b-a+hfrac(fracb-ah)(fracb-a+hh)(frac2(b-a)+hh)6+frac2ah^2b-a+hfrac(fracb-a+hh)(fracb-ah)2+fraca^2hb-a+hbigg(fracb-a+hhbigg)\
&= frac(b-a)(2(b-a)+h)6+a(b-a)+a^2\
Var(X) &= E[X^2] - E[X]^2\
&= frac(b-a)(2(b-a)+h)6+a(b-a)+a^2 - bigg(fraca+b2bigg)^2\
&= frac2(b-a)(2(b-a)+h)+12a(b-a)+12a^212 - frac3(a+b)^212\
&= frac4b^2-4ab+2bh-4ab+4a^2-2ah+12ab-12a^2+12a^2-3a^2-6ab-3b^212\
&= frac(a-b)^2+2h(b-a)12 \
&= frac(b-a)^2+2h(b-a)12\
&= frac(b-a)(b-a+2h)12
endalign*
probability uniform-distribution
probability uniform-distribution
edited Mar 15 at 19:15
VincentN
asked Oct 2 '18 at 14:26
VincentNVincentN
155
155
$begingroup$
Would it help if you knew that $sum_x=0^n x^2 = fracn(n+1)(2n+1)6$?
$endgroup$
– Paul
Oct 2 '18 at 14:33
$begingroup$
It would be helpful for $h = 1$, but I cannot imply it for $hneq1$.
$endgroup$
– VincentN
Oct 2 '18 at 14:36
$begingroup$
You can apply it for $x'=x/h$.
$endgroup$
– Paul
Oct 2 '18 at 14:38
$begingroup$
I don't quite get what you mean by that.
$endgroup$
– VincentN
Oct 2 '18 at 14:53
$begingroup$
I'll put it in an answer.
$endgroup$
– Paul
Oct 2 '18 at 14:57
|
show 1 more comment
$begingroup$
Would it help if you knew that $sum_x=0^n x^2 = fracn(n+1)(2n+1)6$?
$endgroup$
– Paul
Oct 2 '18 at 14:33
$begingroup$
It would be helpful for $h = 1$, but I cannot imply it for $hneq1$.
$endgroup$
– VincentN
Oct 2 '18 at 14:36
$begingroup$
You can apply it for $x'=x/h$.
$endgroup$
– Paul
Oct 2 '18 at 14:38
$begingroup$
I don't quite get what you mean by that.
$endgroup$
– VincentN
Oct 2 '18 at 14:53
$begingroup$
I'll put it in an answer.
$endgroup$
– Paul
Oct 2 '18 at 14:57
$begingroup$
Would it help if you knew that $sum_x=0^n x^2 = fracn(n+1)(2n+1)6$?
$endgroup$
– Paul
Oct 2 '18 at 14:33
$begingroup$
Would it help if you knew that $sum_x=0^n x^2 = fracn(n+1)(2n+1)6$?
$endgroup$
– Paul
Oct 2 '18 at 14:33
$begingroup$
It would be helpful for $h = 1$, but I cannot imply it for $hneq1$.
$endgroup$
– VincentN
Oct 2 '18 at 14:36
$begingroup$
It would be helpful for $h = 1$, but I cannot imply it for $hneq1$.
$endgroup$
– VincentN
Oct 2 '18 at 14:36
$begingroup$
You can apply it for $x'=x/h$.
$endgroup$
– Paul
Oct 2 '18 at 14:38
$begingroup$
You can apply it for $x'=x/h$.
$endgroup$
– Paul
Oct 2 '18 at 14:38
$begingroup$
I don't quite get what you mean by that.
$endgroup$
– VincentN
Oct 2 '18 at 14:53
$begingroup$
I don't quite get what you mean by that.
$endgroup$
– VincentN
Oct 2 '18 at 14:53
$begingroup$
I'll put it in an answer.
$endgroup$
– Paul
Oct 2 '18 at 14:57
$begingroup$
I'll put it in an answer.
$endgroup$
– Paul
Oct 2 '18 at 14:57
|
show 1 more comment
1 Answer
1
active
oldest
votes
$begingroup$
With your edit, you are almost there. You can simplify
$$frachb-a+hsum_k=0^b-a(hk+a)^2$$
$$=frachb-a+hsum_k=0^b-aleft((hk)^2+2ahk+a^2 right)$$
$$=frachb-a+hsum_k=0^b-a(hk)^2+frachb-a+hsum_k=0^b-a(2ahk)+frachb-a+hsum_k=0^b-aa^2$$
$$=frach^3b-a+hsum_k=0^b-ak^2+frac2ah^2b-a+hsum_k=0^b-ak+fraca^2hb-a+hsum_k=0^b-a1$$
For the first term you can apply
$$sum_x=0^n x^2 = fracn(n+1)(2n+1)6$$
and apply the similar formulas that you did previously for the other 2 terms.
$endgroup$
add a comment |
Your Answer
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1 Answer
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1 Answer
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$begingroup$
With your edit, you are almost there. You can simplify
$$frachb-a+hsum_k=0^b-a(hk+a)^2$$
$$=frachb-a+hsum_k=0^b-aleft((hk)^2+2ahk+a^2 right)$$
$$=frachb-a+hsum_k=0^b-a(hk)^2+frachb-a+hsum_k=0^b-a(2ahk)+frachb-a+hsum_k=0^b-aa^2$$
$$=frach^3b-a+hsum_k=0^b-ak^2+frac2ah^2b-a+hsum_k=0^b-ak+fraca^2hb-a+hsum_k=0^b-a1$$
For the first term you can apply
$$sum_x=0^n x^2 = fracn(n+1)(2n+1)6$$
and apply the similar formulas that you did previously for the other 2 terms.
$endgroup$
add a comment |
$begingroup$
With your edit, you are almost there. You can simplify
$$frachb-a+hsum_k=0^b-a(hk+a)^2$$
$$=frachb-a+hsum_k=0^b-aleft((hk)^2+2ahk+a^2 right)$$
$$=frachb-a+hsum_k=0^b-a(hk)^2+frachb-a+hsum_k=0^b-a(2ahk)+frachb-a+hsum_k=0^b-aa^2$$
$$=frach^3b-a+hsum_k=0^b-ak^2+frac2ah^2b-a+hsum_k=0^b-ak+fraca^2hb-a+hsum_k=0^b-a1$$
For the first term you can apply
$$sum_x=0^n x^2 = fracn(n+1)(2n+1)6$$
and apply the similar formulas that you did previously for the other 2 terms.
$endgroup$
add a comment |
$begingroup$
With your edit, you are almost there. You can simplify
$$frachb-a+hsum_k=0^b-a(hk+a)^2$$
$$=frachb-a+hsum_k=0^b-aleft((hk)^2+2ahk+a^2 right)$$
$$=frachb-a+hsum_k=0^b-a(hk)^2+frachb-a+hsum_k=0^b-a(2ahk)+frachb-a+hsum_k=0^b-aa^2$$
$$=frach^3b-a+hsum_k=0^b-ak^2+frac2ah^2b-a+hsum_k=0^b-ak+fraca^2hb-a+hsum_k=0^b-a1$$
For the first term you can apply
$$sum_x=0^n x^2 = fracn(n+1)(2n+1)6$$
and apply the similar formulas that you did previously for the other 2 terms.
$endgroup$
With your edit, you are almost there. You can simplify
$$frachb-a+hsum_k=0^b-a(hk+a)^2$$
$$=frachb-a+hsum_k=0^b-aleft((hk)^2+2ahk+a^2 right)$$
$$=frachb-a+hsum_k=0^b-a(hk)^2+frachb-a+hsum_k=0^b-a(2ahk)+frachb-a+hsum_k=0^b-aa^2$$
$$=frach^3b-a+hsum_k=0^b-ak^2+frac2ah^2b-a+hsum_k=0^b-ak+fraca^2hb-a+hsum_k=0^b-a1$$
For the first term you can apply
$$sum_x=0^n x^2 = fracn(n+1)(2n+1)6$$
and apply the similar formulas that you did previously for the other 2 terms.
answered Oct 2 '18 at 15:08
PaulPaul
6,23721023
6,23721023
add a comment |
add a comment |
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$begingroup$
Would it help if you knew that $sum_x=0^n x^2 = fracn(n+1)(2n+1)6$?
$endgroup$
– Paul
Oct 2 '18 at 14:33
$begingroup$
It would be helpful for $h = 1$, but I cannot imply it for $hneq1$.
$endgroup$
– VincentN
Oct 2 '18 at 14:36
$begingroup$
You can apply it for $x'=x/h$.
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– Paul
Oct 2 '18 at 14:38
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I don't quite get what you mean by that.
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– VincentN
Oct 2 '18 at 14:53
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I'll put it in an answer.
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– Paul
Oct 2 '18 at 14:57