Show that if X is a bounded random variable, then E(X) exists.

In summary, the book claims that if a random variable is bounded, then E(X) exists. However, this is not always the case. The book also claims that if a random variable is bounded and continuous, then E(X) exists.
  • #1
number0
104
0

Homework Statement



Show that if X is a bounded random variable, then E(X) exists.

Homework Equations


The Attempt at a Solution



I am having trouble of finding out where to begin this proof.This is what I got so far:

Suppose X is bounded. Then there exists two numbers a and b such that P(X > b) = 0 and P(X < a) = 0 and P(a <= X <= b) = 1.
I have no idea if I am even doing this right. Anyone wanting to take a crack at this one? Thanks.
 
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  • #2
How do your course materials define a "bounded random variable"? The claim "if X is a bounded random variable, then E(X) exists" isn't true using the usual definition of a "bounded random variable".

Perhaps your problem assumes the domain of X is bounded as well as the range.
 
  • #3
Stephen Tashi said:
How do your course materials define a "bounded random variable"? The claim "if X is a bounded random variable, then E(X) exists" isn't true using the usual definition of a "bounded random variable".

Perhaps your problem assumes the domain of X is bounded as well as the range.

The book specifically defined X as bounded as the following:

|X| < M < ∞ . Here is the whole question, word for word:

Show that if a random variable is bounded—that is, |X| < M < ∞—then
E(X) exists.I do not know about the range though.
 
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  • #4
number0 said:
The book specifically defined X as bounded as the following:

|X| < M < ∞ .

I do not know about the range though.

I see what the book is doing now. I was thinking of a probability density function being "bounded" as meaning it is a function with a bounded range on a possibly infinite domain. Your book means the domain is bounded and you probably get to assume the range of the function is [0,1] or a subset of it. So you can bound the integral of the expression x f(x) by (M)(1) = M.

Have you studied theorems that say something to the effect that bounded (in range) continuous function on a closed interval is integrable?
 
  • #5
start witha a well-behaved continously distributed random variable (no delta functions)

then start with the definition of E(X) in integral form.

You know integral of the distribution function p(x) converges, so can you show the integrand in the expectation is always less than something you know converges eg. xp(x) < c, or xp(x) < cp(x) for all x?
 

What does it mean for a random variable to be bounded?

A bounded random variable is one that has a finite range and cannot take on values beyond a certain limit. This means that the values of the random variable are restricted to a specific interval or set of numbers.

Why is it important to show that a bounded random variable has a defined expected value?

The expected value of a random variable is a measure of its central tendency or average value. It is important to show that a bounded random variable has a defined expected value because it helps in understanding the behavior of the variable and making predictions based on its expected value.

What is the relationship between a bounded random variable and its expected value?

If a random variable is bounded, it means that its values are limited to a specific range. This also means that the expected value of the variable will fall within this range. In other words, the expected value of a bounded random variable will always exist and be within the bounds of the variable's range.

What evidence can be used to show that a random variable is bounded?

To show that a random variable is bounded, one can provide evidence such as the variable's range and any restrictions on its values. This can be done through mathematical proofs or by demonstrating that the variable cannot take on values beyond a certain limit.

Why is it necessary to prove that a bounded random variable has a defined expected value?

Proving that a bounded random variable has a defined expected value is necessary because it provides evidence of the variable's stability and predictability. It also ensures that the variable can be used in statistical analyses and calculations, as the expected value is a crucial component in many statistical formulas and methods.

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