Expectation of X^Y: Estimator & Calculation

  • Context: Graduate 
  • Thread starter Thread starter leehwd
  • Start date Start date
  • Tags Tags
    Expectation
Click For Summary

Discussion Overview

The discussion revolves around the estimation and calculation of the expectation of the expression X^Y, where X and Y are independent and identically distributed (iid) random variables. Participants explore theoretical implications, mathematical reasoning, and specific cases related to this expectation.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant inquires about the estimator for E(X^Y), noting that X and Y are iid random variables with known expectations E(X) and E(Y).
  • Another participant suggests that the initial information provided may be insufficient to determine E(X^Y).
  • A participant proposes that under certain conditions, specifically small variances for X and Y, E(X^Y) could be approximated as E(X)^E(Y) based on a Taylor expansion.
  • Another participant expresses skepticism about the validity of the approximation, indicating that small variances may not be sufficient for the claim to hold true.
  • A different viewpoint argues against the approximation by providing a counterexample involving uniformly distributed random variables, suggesting that E(X^Y) may not equal E(X)^E(Y) in certain cases, particularly when considering distributions that are symmetrical around zero.

Areas of Agreement / Disagreement

Participants do not reach a consensus; multiple competing views remain regarding the validity of the approximation E(X^Y) = E(X)^E(Y) and the conditions under which it may or may not hold.

Contextual Notes

There are limitations regarding the assumptions made about the distributions of X and Y, particularly concerning their variances and the implications of their independence. The discussion also highlights the need for specific examples to clarify the behavior of E(X^Y) under different conditions.

leehwd
Messages
2
Reaction score
0
Can anyone let me know the estimator for the expectaiion of X^Y. X and Y are iid random variables, and their expectation are E(X) and E(Y) respectively.

Thank you.
 
Physics news on Phys.org
I'm pretty sure that's not enough information.
 
Okay, let me put this way. Let E(X) be the expectation of random variable X, and X and Y are independent and identically distributed random variables. My question is, what is E(X^Y)? I did Talyor expansion of X^Y and concluded that, for small variances for X and Y, E(X^Y)=E(X)^E(Y).

Is this correct?
Thank you for your help in advance.
 
It's (probably) true that if the distributions of X and Y are "close" to constant, then then E(X^Y)=E(X)^E(Y) is approximately true.

My gut says that small variances isn't enough, but I haven't done the calculations to be sure.
 
I believe it is not true. Try a simple particular case. For example assume X and Y are uniformly distributed over some interval, and work out E(XY).
A good crazy example would use two intervals symmetrical around 0 (avoid 0 itself), then E(X)E(Y) would be 00, which would be nonsense.
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 1 ·
Replies
1
Views
803
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K