Central Limit Theorem: How does sample size affect the sampling distribution?

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Discussion Overview

The discussion revolves around the Central Limit Theorem (CLT) and its implications regarding how sample size affects the sampling distribution of sample means. Participants explore the theoretical underpinnings of the CLT, the conditions under which it holds, and the practical implications of varying sample sizes in statistical analysis.

Discussion Character

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

Main Points Raised

  • Some participants assert that larger sample sizes increase the likelihood that the sampling distribution of sample means will approximate a normal distribution, as stated by the CLT.
  • One participant mentions that adding an infinite number of small independent factors results in a normal distribution, provided there are no extreme outliers.
  • A Monte Carlo simulation is referenced to illustrate how the sampling distribution approaches normality as sample size increases, with specific examples using a Bernoulli distribution.
  • There is a discussion about the variance of sample means decreasing as sample size increases, with one participant stating that doubling the sample size halves the variance of the sample means.
  • Some participants clarify that changing the sample size results in different random variables, each with its own distribution.
  • There is a debate about the conditions under which the CLT applies, including the necessity for the population distribution to have a mean and variance.
  • One participant challenges the notion that a population with a normal distribution guarantees a normal sampling distribution for small samples, suggesting that the CLT is more robust than that.
  • Another participant introduces the concept of convergence in distribution, specifically how the mean of sample means converges to the population mean.
  • There are discussions about specific distributions, such as the Cauchy distribution, which do not have defined means or variances, and how they relate to the CLT.
  • One participant emphasizes the need for careful distinction between the distribution of the sample and the distribution of the sample means.
  • Conditions for making inferences from samples are outlined, including random sampling, independence, and the normal condition for the sampling distribution of sample means.

Areas of Agreement / Disagreement

Participants generally agree that larger sample sizes lead to a better approximation of the normal distribution for sample means, but there is no consensus on the specific conditions and implications of the CLT, as well as the requirements for the underlying population distribution.

Contextual Notes

Some participants express confusion regarding the conditions necessary for the sampling distribution of sample means to be normal, including sample size requirements and the characteristics of the parent population.

  • #31
Agent Smith said:
@Dale where can I do a Monte Carlo simulation?
I should tell you that there are computer languages and systems that are designed specifically to do Monte Carlo simulations. If you are going to do large simulations, you should look into those.

I would also say that simple problems with analytical solutions are very easy to modify so that the analytical solutions become a nightmare. In those cases, Monte Carlo estimates are often much easier to get and to be confident of. Even if analytical solutions are still possible, the Monti Carlo estimate can provide a good "sanity check" for the analysis.
For instance, suppose in the coin toss example we added the requirement that a Head will not count if 3 of the prior 5 tosses were Heads. That would be trivial to add to the Monte Carlo simulation, but the analytical solution would be more difficult. Although this example seems artificial, the real world often gets complicated like that.
 
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  • #32
Agent Smith said:
Should I have written ##\displaystyle \lim_{n \to \infty} \frac{1}{n} \sum_{i = 1} ^n \overline x_i = \mu##? In words, the mean of the sample means approaches the true mean of the population as the number of samples approaches infinity. Not sure if that's the actual statement or not. How would you write down the correct expression? @Dale

What about my question regarding the sample size? Why do we assume the population is infinite?
we say that the sample mean converges in probability to the population mean: that is, given n epsilon, it is true that the limit as n goes to infinity of P(|Xbar - mu| > epsilon) = 0 (or, equivalently, the limit of
P(|Xbar - mu| <= epsilon) = 1).


It's only when the sequence is standardized as done in other posts that the normal distribution comes into play.
 
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