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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Is this a Random or Purposive Sample? Inclusion-Exclusion Criteria and the Sampling Frame

Introduction I am confused about when a sample is a random sample (i.e. probability sample) and when it is a purposive sample (i.e. non-probability sample). My understanding is that the former allows ...
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10 views

Choosing which distribution is most accurate

Let's say we have two samples from different normal distributions and we want to determine which distribution is most accurate relative to an ideal value. How would we evaluate which one is more ...
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33 views

Chi-square test on a sample from population having an unequal distribution

I got a sample with an unequal gender distribution ($30$ males to $200$ female). This distribution is quite "representative" for the population the sample is taken from. Nevertheless, in a paper, ...
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33 views

must be a representative sample to apply factor analysis?

To apply the exploratory or confirmatory factor analysis, is what we should select a representative sample? And is there any condition to select this sample? I would validate a translated ...
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12 views

Estimating Sample Weights

I have a number of raw counts of people across a couple of different dimensions: hour and web site. The data I have is not the full set of people, though. Instead, I am using the raw data I have ...
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13 views

Negative samples on multiclass neural network training

I want to train a deep neural network to classify images. In every implementation I have seen, multiclass training uses only the positive examples for each class. Is there any way to utilize ...
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45 views

How to make sample space of the following question

My teacher gave me a question to solve.In the book of Ronald E. Walpole (Probability and Statistics for Engineers and Scientists), chapter no#3 exercise 1,question #2 which is as below: 3.2) An ...
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24 views

Finding a confidence interval for observations being outliers

Suppose I have a sample with sample size $N$ that is obtained experimentally, e.g. I have counted the number of birds at a certain location at a certain time. Now suppose that the sample (the number ...
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16 views

Regression with Aggregate data: no interest in individual behaviour

First of all, I am very glad I came across this forum as it looks useful and friendly. In advance, thank you for the time you will spend just reading my questions. So here it comes: I work on a ...
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11 views

(Pretty) large sample size, unequal variance, unequal sample sizes, non-normal distribution. T-test alternative?

So, I've never had all these problems at the same time before, but I have: - Likert data, from a 9 point scale - n = 317 v 177 respectively - SD = 2.08 v. .274; 1.9 v. 2.6; 2.5 v. 2.9 etc. (you get ...
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34 views

Transform sample to achieve target mean, skewness, etc

I have a sample of data with N values from which I calculate basic moments such as mean, standard deviation and skewness. I will then change these moments to different values according to my own ...
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24 views

Study design: equal/unequal sample sizes

I have recently sent a paper on aflatoxin levels in nuts for publishing. The aim of the study was to analyze a total amount of 106 nuts. The nuts were divided into four categories: walnuts (n=33), ...
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14 views

Sample calculation

I'm about to start an In vitro model experiment. I will have 3 groups to compare between them with continuous variables. I will use ANOVA for the comparison and I would like alpha to be 0.05 with ...
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15 views

Accuracy of approximation to sample median

Suppose we sample $n$ real numbers uniformly on $[a, b]$. We wish to find the sample median, but we will approximate it as follows: randomly choose a subset of the sample of size $k$ with uniform ...
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18 views

help with sample size calculation

hi im conducting a study on a certain ratio in a blood exam (lets call it X) . I aim to say that there is a certain sensitivity (let say>80%) for people to be sick if X>10. (my actual intent is to ...
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21 views

Test if 2 samples are taken from the same population (multi-dimensional data) - worked example

I'm looking to learn (not just apply) how to test is two samples are drawn from a single population. The data I'm likely to apply this to is multi-dimensional so that's my target. Can anyone give me a ...
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2answers
32 views

sample versus population in experimental data

I am not statistically oriented, so I am hoping you might be able to help. I have a small lab setup that mimics a larger natural process (natural disaster). I have designed and completed 46 ...
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1answer
307 views

How to detect random clicks on a page?

I have been tasked with detecting if a bot is clicking randomly around a web page. I was thinking of splitting up the web page into 20 by 20 pixel squares, and then assigning each click to a square ...
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8 views

Observations independence

I have observed prices of products (phone plans) that appear in the market in each year during 8-year period. When the product is on the market, its price doesn't change. For such products, when price ...
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58 views

How to validate if a sample is independent and identically distributed

How can I check if the data is drawn i.i.d. from an unknown multivariate distribution?
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36 views

Using sample standard deviation to estimate the standard error

In single-sample hypothesis testing, we can collect a sample and test whether the mean of this sample might have been drawn from the same population as some hypothesised mean. We use the standard ...
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33 views

Why is the every data item in a sample is considered to be produced by a different random variable?

In the stats book I am studying, while explaining bias and mean, the author goes like this: "... Suppose a sample $$S=(X_1, X_2,...,X_n)$$ has been collected. ... Sample mean $\bar{X}$ estimates ...
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2answers
103 views

How do i derive the joint probability distribution table of X and Y?

If there is a bag with 3 red balls, 2 blue balls and 1 white ball. Two balls are drawn without replacement. Let X be number of red balls drawn and Y be number of blue balls drawn.
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82 views

Calculating $\overline{X}$ and $S(X)$ for a truncated Normal distribution

I have the following dataset which appears to be normally distributed but is truncated at 0. If I ignore the values which are 0 I get an even better distribituion. I would like to conclude that ...
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116 views

Correcting biased survey results

Knowing that a population sample (non-random) is biased in terms of its demographics, what are the best practices to correct for this issue? That is, let's say that I can attach an array of ...
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65 views

How to evaluate similarity of datasets based on summary data?

I have summary data that I want to compare to my own data. For the summary data I do not have access to the underlying data, however, I know the percentiles as shown below (A). I also calculated ...
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42 views

Need Help w/ Research Proposal

I am currently doing a master's research proposal (experiment hasn't been completed yet) and need to decide what statistical test to use. My research question is observing increases in bowling ...
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30 views

Are identical samples independent?

Are results of two different tests performed on exact same sample independent or dependent? For example, if the same group of rats were injected some drug A, results collected, then long enough time ...
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28 views

Sampling Size for a large Dataset

I am having a dataset of size upwards of 200 million rows. I have no knowledge of the distribution of this dataset. Would like to perform some analysis on this - like look at the ...
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1answer
23 views

Statistics - (bivariate data) Planning an Inquiry

I have to conduct a statistical inquiry that is representative of a population. You have to choose from a list of situations, and my choice was to measure the weight and length of carrots. The ...
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31 views

How to use/interpret bootstrapping?

I am working on an stochastic optimization problem. Now I have come across the idea of using Monte Carlo sampling approach to solve it. I need the empirical distribution or the true distribution of ...
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66 views

How to calculate sample size for this study design?

I am trying to find out whether the number of participants I recruited (N=42) so far is sufficient for my study in which: there are two interfaces (say A and B). ALL students in the study will try the ...
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18 views

Prior Probabilities vs Sampling

In case i have a dataset which has 100000 records and only 10000 of them represent Churn cases. Hence before building a predictive model i set a prior probability as 10% for CHURN and 90% for NON ...
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67 views

Number of different combinations in a sample

I hail from Mathematica SE. A friend of mine asked me a statistics question (I'm an economist and am assumed to know such things) which kind of stumped me, since I usually deal with non-discrete ...
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34 views

How to report sample size of an experimental study in a thesis based on power analysis?

I am not sure whether I have reported the sample size properly in my thesis which I have calculated based on power analysis. Please a have look: Based on a power analysis, the desired sample size ...
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213 views

Why doesn't the standard deviation represent a normal distribution?

Why doesn't the standard deviation of a sufficiently large sample represent a normal distribution that we can make inferences from? Let me list my thought process, so hopefully someone can highlight ...
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23 views

sample size power calculation

This is probably very simple but I am struggling...in a population there is a disease present clinically in around 35% of patients, we want to use two tests which when used in parallel have a ...
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1answer
97 views

Cohen's d in proportion test

I am calculating the sample size for proportion test. I would like to have significance level =0.05, power = 0.90 and that the effect size is greater that 5%. I would like to have statistically ...
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1answer
43 views

Sample size problem

I am looking for a suggestions on how to estimate the sample size in such a problem. There is a group with one usefull treatment (let's say 10 milion people) but one consider if there might be more ...
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77 views

Distribution of distributions

Could anybody point me towards material for dealing with data when your sample points are distributions in themselves? To be more specific each data point I am sampling has a mean and a variance, so I ...
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1answer
42 views

The difference between the standard error of the sample and the standard error of the mean value

I have an assignment that gives 48 counts of the same phenomena occurring over the same time interval. I am asked to a) Calculate the mean of the counts b) Calculate the standard error of the sample ...
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1answer
47 views

What is a draw from a Dirichlet Process?

I know a draw from a K-D Dirichlet distribution is a probability vector of dimension K. But still it's not clear what is a draw from a Dirichlet Process. What I understood is that a draw from a ...
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1answer
28 views

How can I show that my sample is random and a good representation of the population?

Okay, I'm looking at a population of user reviews. I have collected a random sample of the reviews and studied the trends of the words used and sentence structure. How do I make inferences about ...
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29 views

Performing a comparison between a sample distribution and population distribution in excel or nvivo

What is a relatively easy stats test to perform in excel/nvivo that is arguably reliable and valid and a good method for comparing a sample's normal distribution with a population's normal ...
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1answer
23 views

Running regressions on subsamples: Include the variable on which the subsample is based in the regressions?

Income is one of my independent variables in a sample of 2000 households. I'd like split the sample along household income lines (poor, vulnerable and non-poor). Is there a reason not to include ...
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1answer
107 views

Mutual Exclusivity

Suppose that a study is being done on all families with one, two, or three children. Let the outcomes of the study be the genders of the children in descending order of their age. A. List sample ...
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144 views

Finding the sample space of an experiment

Suppose that a study is being done on all families with one, two, or three children. Let the outcomes of the study be the genders of the children in descending order of their age. List the sample ...
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24 views

How to simulate a sample with density $f^p / \int f^p$?

Given a density $f$ (or given a $n$-sample $X_1, \ldots, X_n$ with density $f$), is there a way to create a $n'$-sample $X_{p,1}, \ldots, X_{p,n'}$ with density $f^p / \int f^p$, where $p \in ...
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19 views

Minimum sample size in nonparametric data

My population has more or less 80,000 individuals and I would like to take a small sample with a high probability it is really close to the whole population. The problem is that my data is ...
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17 views

probability of sample proportion

I am trying to find the z-score for a sample proportion of 0.39 (The question is actually asking to find the probability of the sample proportion that is greater than .39). The only information ...