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Solved – Finding the mean and standard deviation of an unknown distribution from a sample

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I am interested in finding the mean and standard deviation of the whole distribution by looking only at a random sample. I don't know anything else about the distribution (for example I don't know if the distribution is normal or not). Is what I'm asking even possible? Best Answer Sure, your best guess of the … Read more

Solved – Out-of-time testing (basic question)

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I understand the importance of out-of-sample testing, but could you tell me why I should (or shouldn't) do out-of-time testing ? The only use that comes to mind is if the predictive model applies to economic activity and seeing whether it would work in both bull and bear markets. But more insight in the use … Read more

Solved – Out-of-time testing (basic question)

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I understand the importance of out-of-sample testing, but could you tell me why I should (or shouldn't) do out-of-time testing ? The only use that comes to mind is if the predictive model applies to economic activity and seeing whether it would work in both bull and bear markets. But more insight in the use … Read more

Solved – How to deal with non random samples

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I have a specific question about random selection, representativeness and inference. It is well known that it's necessary to use random selection to get representative samples from the population of interest. But what happens with non-random samples? I am working with an intentional sample. I compared the means of some of the main variables of … Read more

Solved – Why doesn’t a sample proportion also have a binomial distribution

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In a binomial setting, the random variable, X, that gives the number of successes is binomially distributed. The sample proportion can then be calculated as $frac{X}{n}$ where $n$ is your sample size. My textbook states that This proportion does not have a binomial distribution however since $frac{X}{n}$ is simply a scaled version of a binomially … Read more

Solved – Proof that $mathrm{E}(s^2) = sigma^2 cdot N/(N-1)$

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What's the derivation for expected value for sample variance for a sample taken from simple random sampling without replacement, i.e., how do we show that $$mathrm{E}(s^2) = sigma^2 frac{N}{N-1}$$ Is my assumption this only applies to SRS samples without replacements correct? On a related note, how is the sample variance from two numbers, $x_1, x_2$ … Read more