Estimation error from estimation quantile of normal distribution

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Discussion Overview

The discussion revolves around estimating the probability that a normally distributed random variable exceeds a quantile estimated from a limited number of observations. Participants explore the implications of unknown mean and variance in this context, as well as the methods for estimating quantiles based on sample data.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks validation for their approach to estimating the probability related to a quantile of a normal distribution and questions how to account for unknown mean and variance.
  • Another participant suggests that instead of estimating the quantile directly, one should first estimate the mean and standard deviation, arguing this leads to better estimates, especially for large deviations from the mean.
  • A third participant agrees with the previous suggestion and elaborates on the statistical properties of the sample mean, noting that it is t-distributed when the standard deviation is unknown and discussing the Central Limit Theorem (CLT) for larger sample sizes.
  • Another participant posits that the project may focus on understanding the distribution of a specific estimator rather than optimizing quantile estimation, highlighting the difference between practical and academic approaches in project objectives.

Areas of Agreement / Disagreement

Participants express differing views on the best approach to estimating quantiles and the implications of unknown parameters. There is no consensus on a single method or perspective, indicating ongoing debate and exploration of the topic.

Contextual Notes

Participants mention various statistical distributions and methods, but there are unresolved assumptions regarding the sample size and the specific context of the estimation problem. The discussion does not clarify the exact nature of the estimator in question.

Derk
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Hi guys,

For my (master) project I am trying to find the probability that a random variable, which is normally distributed, exceeds a quantile that is estimated by a limited number of observations. See attached for my attempt.
- Is it correct?
- How to incorporate the fact that the mean and variance of the normal distribution are unknown in reality?

Thanks in advance!
 

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Why do you estimate it that way if you know your variable has a normal distribution? Find estimates of the mean and the standard deviation, calculate the quantile based on that. It will give you much better estimates especially for large deviations from the mean.
 
I agree with mfb: If/when you don't know the standard deviation from a normal population, then the sample mean ##x_s ## is t-distributed as ( for a two-sided) ##( x_s- t_{ \alpha/2}SE, x_s+ t_{\alpha /2} SE )## where SE is the standard error and ## \alpha ## is the confidence level. Other statistics have different distributions. Do you have any specific one in mind? If you are computing the sampling mean and your sample is large-enough ( n>30 usually; n>= 40 for more accuracy) then you can use the CLT to assume normality.
 
It may be that the purpose of @Derk 's project is not to find an optimal method of estimating a quantile, but rather to work out the distribution of a particular estimator. If he were doing a masters project in engineering, we'd expect something practical, but a mathematical project can be an "academic exercise".
 

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