Stochastic convergence

carla1985

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Apr 14, 2013
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Hi, I'm really stuck on this last question for one of my stats papers, can anyone help on it please? Thanks:

"(i) Let X be a random variable on a discrete probability space (Ω, A, P ) and let \(\displaystyle \epsilon>\epsilon_0\). Show that
\(\displaystyle P(|X-a|\geq\epsilon)\leq P(|X-a|\geq\epsilon_0)\) for real and positive \(\displaystyle a\). Why is this useful when checking on stochastic convergence?

(ii) Let \(\displaystyle X_n\ for\ n\in N_0\), be a collection of random variables such that each \(\displaystyle X_n\) takes values in the set {3, 8, 11} with the distribution of
\(\displaystyle X_n\) given by

\(\displaystyle p_{X_n}(3)=1-\frac{3}{n}-\frac{5}{n^2},\ \ \ P_{X_n}(8)=\frac{3}{n},\ \ \ P_{X_n}(11)=\frac{5}{n^2}\)

Prove that \(\displaystyle X_n\)3 stochastically as n → ∞."


 
Hi, I'm really stuck on this last question for one of my stats papers, can anyone help on it please? Thanks:

"(i) Let X be a random variable on a discrete probability space (Ω, A, P ) and let \(\displaystyle \epsilon>\epsilon_0\). Show that
\(\displaystyle P(|X-a|\geq\epsilon)\leq P(|X-a|\geq\epsilon_0)\) for real and positive \(\displaystyle a\). Why is this useful when checking on stochastic convergence?

(ii) Let \(\displaystyle X_n\ for\ n\in N_0\), be a collection of random variables such that each \(\displaystyle X_n\) takes values in the set {3, 8, 11} with the distribution of
\(\displaystyle X_n\) given by

\(\displaystyle p_{X_n}(3)=1-\frac{3}{n}-\frac{5}{n^2},\ \ \ P_{X_n}(8)=\frac{3}{n},\ \ \ P_{X_n}(11)=\frac{5}{n^2}\)

Prove that \(\displaystyle X_n\)3 stochastically as n → ∞."


What are your thoughts?

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Sorry, it took me so long to figure out the tex stuff i forgot about what else i needed to put in there. Ok, the first part im unsure how to start really, logic tells me its true but i dont know how to show it.

for part ii i thought i thought i should add them up and divide by 3 but i get a third. Then i tried taking the limits of the 3 individual functions but that gives me 1 so either my maths is terrible or im using the wrong methods. Any pointers in the right direction is very much appreciated.
 
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