# Questions tagged [sample]

A sample is a subset of a population. Statistics, in general, is concerned with using samples to make inference about the parameters governing a larger (possibly infinite) population.

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### Calculating sample size with standard deviation?

Okay so I have an exam coming up pretty soon and I really can't get the hang of how to calculate sample size when all you are given is standard deviation. For instance: A normal population has a ...
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### Sample size for uniform multinomial to control minimum

I'm interested in controlling the minimum for a uniform multinomial distribution. Specifically, What would be the sample size to have the following inequality regarding the minimum? Do you know of ...
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### I Need Help!!! I can't understand this statistics homework! [closed]

In an election, suppose that 55% of voters support creating a new fire district. If we poll 163 of these voters at random, the probability distribution for the proportion of the polled voters that ...
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### Is a non stratified survey sample 70,000 people sufficient to make conclusions about a population of 12 million people?

Is a survey with a sample size of 70,000 people sufficient to make conclusions about a population of 12 million people when there is no way to ensure that the sample is stratified sample where the ...
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### Which statistical tests can I use to analyse significant difference between the means of non-random samples? [duplicate]

I want to compare the means of non-random samples to population mean. However, most standard tests (eg. t-tests, ANOVA, Welch test etc.) are based on the assumption that samples are randomly obtained ...
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### unknown standard deviation = range/4

Suppose you want to estimate the average age of all Boeing 737-300 airplanes now in active domestic U.S. service. You want to be 95% confident, and you want your estimate to be within one year of the ...
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### sigma is unknown, so it must be estimated by using sigma approximately equals (1/4) * (range) [duplicate]

Suppose you want to estimate the average age of all Boeing 737-300 airplanes now in active domestic U.S. service. You want to be 95% confident, and you want your estimate to be within one year of the ...
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### Bayesian posterior guarantees [duplicate]

I have a quantity that I know before hand is a constant. The instrument used to measure this quantity creates measurements that are noisy with zero bias. Suppose the constant is $c$ then the ...
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### How to derive p value of whether there exists a difference (given before and after correlation, averages, and standard deviations)?

I am trying to solve the following question: A chemical refining process is monitored before and after the plant is shut down and cleaned. At 40 randomly selected outputs, before cleaning, ...
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### Representativeness of sample, distribution of age from sample compared to national sample

Please forgive my entry-level question. I have been slamming my head on the table for well over 3 hours now as I cannot seem to figure this one out. I have a sample of n=450, population is about 17m....
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### split (or better full sample) dataframe with conditions

I'm pretty new to R and this kind of tasks, I'm deeply sorry if the question is not correct or malformed: I have some data in Excel, like the following: ...
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### How to estimate log-normal distribution parameters from a set of data?

I don't have any background in statistics, so maybe I may say things that are incorrect. I have to model the production of waste deposition at each container of a set of containers and I have access ...
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### Sample Variance Quandry [duplicate]

I was working on an explicit example for a student of mine, and I ran into a bump. Assume that the population is $\{1,2,4\}$. I draw samples of size 2 (without replacement) from the population. From ...
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### how to infer population proportion from samples from 2 disjoint subgroups?

Suppose that I know that a large population consists of equal numbers of men and women. I sample 1000 men and ask whether they have ever eaten an avocado. Some number M say yes. Then I sample 1000 ...
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### One Point Sample Size Information [duplicate]

Is there ever a 1 person sample size? Is there a 1 sample size for a computer program? When does a 1 data point sample size make sense?
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### Sample Variance and Dividing by $n-1$

In this video... https://www.youtube.com/watch?v=sHRBg6BhKjI ...and in many others, the explanation for why when calculating the sample variance we divide by $n-1$ instead of by $n$ is the following:...
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### Can we tell anything at all about $\frac {S_n^2}{\sigma^2}$ if we know that the distribution is normal?

Suppose we don't know anything about a distribution except that it is a Normal distribution with mean $\mu$ and variance $\sigma^2$. Can we argue, theoretically, the sample variance, $S_n^2$ ...
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### Determining Sample Size When Low Probability Items Are Of Interest [closed]

Let's assume there are 10,000,000 Yankee fans and we want to analyze what else these 10 million people are fans of. A simple question is, what sample size do we need to be confident in the results? ...
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### Rather use a sample of a population or analyze a whole population but smaller?

I am validating an automated surveillance program. It is about infection incidence on a hospital ward. I could easily check if the small list of infections produced by the automated surveillance ...
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### Distribution of the sample variance $S^2$ from a normal population [closed]

Let $X_1, X_2, X_3, ….., X_n$ be $N(\mu, \sigma^2)$ distributed. Then what is the distribution of $S^2$ I have already proven that if $X_i$ are $N(\mu, \sigma^2)$, then $\frac{(n-1)S^2}{\sigma^2}$ ...
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### Weird sample variance when creating a lognromal sample with pre-defined mean and variance [duplicate]

I have been working with lognormal distributions as a proposal distribution for some MCMC routines which require the proposal distribution to have some pre-defined sample mean and variance, $m$ and $v$...
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### Is this a valid way to get a simple random sample?

I have a data set of about 200,000 observations about establishments in my district and their operating time. I need to establish the correctness of my data. Consequently, I am trying to take a simple ...