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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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How many parameters are in this specific model

I am planning on doing Structural Equation modeling on the following model that is pictured: I am trying to calculate my needed sample size. I have read the rule of thumb is 200 for SEM or 20 cases ...
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35 views

Index accuracy based on sample size out of population size

Suppose I have people who work at different companies and I am interested in seeing their view on some topic. In order to do this, I decide to conduct interviews on people from each of the different ...
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How to sample from a multivariate uniform distribution with constrained sum [closed]

Problem description: Let say that we have the following 4 uniform distributions: $u_1$~$U_1(-1, 1), u_2$~$U_2(0, 2)$, $u_3$~$U_3(0, 0.2)$ and $u$~$U[U_1, U_2, U_3]$ subject to $u_1 + u_2 + u_3 = 1$. ...
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Estimate mean from sample data

Assuming a sufficiently large set of data, is there a formula for "predicting" a mean value with a certain degree of accuracy without calculating the mean for the whole set of data? Example, say I ...
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Why is it necessary to assume that a sample vector consists of n sample variables instead of assuming that we have a sample of size n?

This is a very basic question, but I need help to grasp the concept. From what I understand: If I carry out a survey on body weight, every single answer to the question "How much do you weigh?" is a ...
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Check if data set is drawn from a distribution/Check if sample is representative

I have a data set $X$ and there is another sample $Y$. I suspect that $Y$ is a subsample of $X$ and I want to check that hypothesis. Obviously, both contain the same number of variables (data types ...
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Calculating the variance of sample, knowing the mean of population

Suppose that I somehow know the mean of the population. And I want to calculate the variance of a sample. Should I subtract population mean or sample mean? Is there any situation in which I should use ...
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What is the impact of seed weights in raking (iterative proportional fitting)?

In survey weighting, I've seen that first a design weight adjustment is made (to reflect over- or under-sampling), and then a non-response adjustment is made (to reflect groups that are less likely to ...
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For what reasons should one use Bootstrap Testing when the sample size is large?

Bootstrap testing is great if we have a small sample size where the Central Limit Theorem does not apply. However, what are convincing reasons we should use Bootstrap if we do have a large sample size....
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Creating sample data set of quiz with n number of questions and set number of students using R

I am very new to R and statistics. What I am trying to do is create some sample data sets of quizzes with n number of questions that the x number of students get correct. Using this, I would like to ...
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What are the different algorithms/code to reconstruct a sampled network traffic data

My sampling rate is 1/1000 for netflow data. May I know what is the suggested algorithm/codes to reconstruct this data? Thanks,
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28 views

Ratio of cases to controls in retrospective cohort study

I am conducting a retrospective cohort study in which I have 10,000 cases with exposure to X, and a very large control population (10,000,000+ subjects) without exposure. I am taking an individual ...
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71 views

Can the Bayesian but not the frequentist “just add more observations”?

Since the frequentist's p-values are uniformly distributed under the null hypothesis, it is a highly problematic practice to add more and more data to your sample until you find a significant result. ...
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what will be the result of sum of several samples with different probabilities?

I have a graph and initialize its weights with normal PDFs. what i'm trying to do with this graph is to find the longest path for different samples of the weights. samples of weights of the graph so ...
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Significance Testing with Known Control-like Contamination in Test Group

Spent a lot of time searching and haven't found an answer - apologies if this was asked before worded differently. I have a somewhat messy experiment that has already been conducted with large test ...
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How to estimate sample mean/variance from another, smaller sample?

Let's say I record some variable from Sample 1 of size = 10 and find that mean = 10 and ...
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1answer
52 views

Two dice roll with {1,2,3,4,5,6} and {10,20,30,40,50,60} and importance of RV mapping

We're all too familiar with a two-dice-roll experiment where we start with a uniform sample space of $S_{die}=\{1,2,3,4,5,6\}$ and end up in a non-uniform pmf for the sum of the numbers on the two ...
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How is sample mean divided by sample STD distributed for normal distributions?

Let's assume that we sample N times from a normal distribution with known mean and variance. With a generated sample we calculate sample mean and sample standard deviation. Then we divide sample mean ...
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Time series: sample vs. population, population vs. realizations of random process

Suppose we have 120 monthly observations (Jan 2000 - Dec 2009) of unemployment rate and suppose we would like to use these in order understand the unknown underlying stochastic process that generated ...
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How is the Akaike information criterion (AIC) affected by sample size?

I am evaluating several logistic regression models predicting college student retention. I am using some basic and well-established predictors, such as high school GPA and SAT scores. I understand ...
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2answers
128 views

How do I compare means when I have a sample and the whole population?

I have the following didactical exercise to carry out: Scenario I have the avg room price for all the hotels of my chain (32 observations of the 32 hotels). Then I have the avg room price for a ...
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51 views

What is the probability that sample variance decreases by adding random Gaussian noise to the variable?

If we assume WLOG that our variable X has mean zero (mean-centered), then this can be stated $Pr \bigg(\sum x^2 > \sum (x-n)^2 \bigg)$ for some random variable $n$ distributed under $N \sim N(0, \...
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Calculating sampling proportion's standard deviation given population proportion?

So the question is as follows (paraphrased): A population votes for/against a political candidate. In a sample of 200 voters, let $X$ be the fraction of people who vote for this candidate. ...
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1answer
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How to test for significant correlation while controlling for sample size?

Creating a SLR model and performing a t-test on the slope parameter (or doing an F-test on the sum of squares) greatly depends on the sample size. I am dealing with very large sample sizes, so small ...
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1answer
54 views

Dealing with small sample size

The objective is to classify a variable Y which is binary, outcomes [0,1], where all the features $X_1$....$X_{156}$ are normalized and continuous. The methods I'm using are Logistic regression and ...
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1answer
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Evaluating usefulness of estimations of a parameter for different distributions

If I had a sample of size n and wished to estimate some parameter, say p for two different distributions from the produced sample what would be required to determine which was more useful? Assume the ...
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Likelihood that two random sample sets come from the same population

I have two random sample sets of 100 points, with 7 possible answers (A – G) each. The sets are as follows: Set 1 A 49 B 22 C 14 D 7 E 4 F 4 G 0 Set 2 ...
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Confront Distribution of 2 samples

I found this problem during an interview, and I have little or no clue on how to proceed. Say you have two samples, of different length: ...
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1answer
37 views

Is there a distribution that matches my data?

I am not an experienced statistician, typically only dealing with normally distributed data. I would like to know if the following data sample can be represented by a well-known distribution? If so, ...
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Why under constant sample size I can get different guarantees on Type I and Type 2 errors, and MDE

I have been tricked by this basic question on hypothesis testing. Imagine you are setting up an experiment. The sample size is a function of the minimum detectable effect and the guarantees that you ...
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How to test the difference in mean between a group and a sub-sample of the group?

A year ago some of my colleagues made a rapport for a client in which they were to report the mean of approximately 100 students examination grades. Here a year after the client has found the ...
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32 views

Sample size confidence limit

I'm reading this text and wanted to know how they calculated the 95% confidence interval when calculating sample size and what it means: "The sample size is 150 so that for a response rate of 80% ...
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How to do sample size calculation?

We are trying to use Binomial CDF to calculate sample size (assuming population size is infinite). However, we can only set confidence level, tolerable deviation rate and have no idea of how to get ...
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1answer
44 views

Confidence interval on binomial distribution on one sample predicted from another sample

I have a work problem that seems to match pretty much exactly the "drawing balls from urns" type of problem, and it must be a pretty common type of problem, but my googling didn't find a solution. I ...
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25 views

Increase the number of samples when the PDF is invariant

Background: $$\frac{\partial C}{\partial t} = D \frac{\partial^2 C}{\partial x^2}$$ is given by Fick's second law, in which $D$ is the diffusion coefficient. The solution to this equation (given the ...
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2answers
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What's the recommended approach when using hypothesis tests on a large sample dataset (1M+)?

What's the recommended approach when using hypothesis tests on a large sample dataset? Talking about 1M+ records. According to this post (http://blog.minitab.com/blog/statistics-and-quality-data-...
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126 views

About Sampling and Random Variables

So I've recently started an introductory course in econometrics and I'm having trouble grasping the idea of Random Variables and Sample distributions If we have a population and we take a sample $Y= \...
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Random (?) number generation in R using sample() always returning the same result [closed]

I am writing an R script (using RStudio on Ubuntu 18.04), and at a certain point I need to randomly pick (with no replacement) 123 random numbers between 1 and 1040. I do this with: ...
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Is the distribution of a random sample the same as the distribution of a population?

I need to simulate 365 million random numbers from a t distribution with given parameters in python. I need to simulate 1 million years each consisting 365 days and for each day I need a random ...
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15 views

Sample size for comparing two properties of time series data

I have a dataset of observations of two properties of an object (x and y), which are distributed over time, ...
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31 views

How to sample a vector from Multivariate normal with the last element constraint to positive?

I'm doing MCMC simulation and a posterior is hard to sample. Suppose I need to sample a vector $\beta \sim N(M_{\beta} , \Sigma_{\beta})1_{\beta_{K}>0}$, which mean $\beta$ is a vector with length ...
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45 views

Comparing sample correlation coefficient with population correlation coefficient

Assume there is a population, P, of size N. Each member of the population has three variables associated with it, a nominal variable C (with m unique categories), and two continuous variables X and Y....
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Update to estimate of population mean based upon new sample

Suppose I sample some phenomenon with a potentially moving mean, let's say height of males on their 18th birthday, and I run this survey every year. Each year I produce a sample mean of height, which ...
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159 views

How do sample weights work in classification models?

What does it mean to provide weights to each sample in a classification algorithm? How does a classification algorithm (eg. Logistic regression, SVM) use weights to give more emphasis to certain ...
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29 views

Why don't we use the n-1 correction for standard error of sample proportion?

From my understanding, when we construct a confidence interval for a sample mean with a sample size of n, we try to estimate the standard deviation of the sampling distribution $$σ_{\overline{x}} = \...
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1answer
43 views

Is this conclusion drawn from sample or population?

"When asked what they would use if they were marooned on an island with only one choice for a pain reliever, more doctors chose A than B, C or D." Is this conclusion drawn from population or a sample?...
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Population Stability Index: Why ln not log? [duplicate]

The Population stability index is based on natural logarithm. http://ucanalytics.com/blogs/population-stability-index-psi-banking-case-study/ The formula looks somewhat similar to what I have seen ...
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Dilemma concerning prediction of user satisfaction

Imagine that you have data with information about users : Age, sex, location, etc ... with the answer to two additional questions : Q1 = Have you tried product P ? yes/no ; Q2 = Did you enjoy product ...
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What test to use to prove one sample is significantly different

I am studying performance of football teams. I want to prove one team is significantly more successful at home then other teams. I calculate the ratio between points per game at home and points per ...
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Implications of sample size increasing over time

I have apartment data on rents from 2000 to 2016 where the unit of observation is an individual property. The sampling methodology included more properties as time went on thereby expanding the ...