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 to check if a sample is representative or not biased?

We are studying the difference in behavior between genders on an online community. We are only interested on those users who participate in the site and whose gender could be easily inferred by other ...
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357 views

Still confused with the p-value definition

The p-value is defined as the probability, under the assumption of the null hypothesis H, of obtaining a result equal to or more extreme than what was actually observed. A p-value lower ...
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61 views

Advantages and disadvantages of using population and samples for statistics

I need to know the advantages and disadvantages of using a sample or a population to collect data. I understand what a sample is and what a population is, but I do not know what the advantages and ...
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40 views

Comparing two populations [Beginner]

I have sampled from two separate populations, and I want to figure out which population is better. Population 1 has an average score of 84.1 and a standard deviation of 11.8. Population 2 has an ...
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10 views

Filling in “gaps” in Sample data from universal data

Quick background - I have a BS in mathematics, and have just recently started a position related to data science (nothing heavy, but requires enough simple statistical analysis that I find myself ...
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22 views

Sample size and Central Limit theorem

I'm working on an example in introductory statistics and I'm not sure if my answer is correct. I think 2,3,5 is correct and not sure about 1,4. Am I correct? It's about choosing correct statements ...
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23 views

What sample size is needed to estimate the population mean, with unknown variance?

I want to know what's the sample size needed to estimate the population mean, with unknown variance? I'm filling up a database that stores the values of wifi-accespoints' strength level at certain ...
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4answers
35 views

Sample size of sampling distribution of the sample mean

When people say that the mean of the sampling distribution of the sample mean is equal to the population mean, is this true regardless of how small or large the size of the samples are? I'm having a ...
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13 views

validity when between subjects factor makes group size uneven

I'm doing a repeated measures analysis and, while I have even amounts of samples for each subject, and the variances and sphericity are fine for the dependent measures, I'm worried because I have ...
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1answer
38 views

How to create matched sample for sample selection method to perform?

I'm working on a project in which I only use sub sample (say the immigrant households of all households), and there is a sample selection problem that I apply the standard Heckman's sample selection ...
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1answer
45 views

Analyzing data while collecting the data

Part of our samlpe has been collected (Phase 1, $n=12$ subjects with measurements pre and post treatments). The remaining sample (Phase 2 with another 8-10 subjects) will be collected in a few months. ...
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1answer
49 views

Sample size for categorical data

I have a population of phone calls - 200,000. There are different reasons for each call, but lets assume the number of reasons is known. i.e. 7 different call reasons: 1) Check on order 2) Cancel ...
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3answers
39 views

Inference about parameter $\theta$ be same?

Let $\mathbf x$ be a sample point and $T(\mathbf x)$ be a statistic of $\mathbf x$. Similarly, let $\mathbf y$ be a sample point and $T(\mathbf y)$ be a statistic of $\mathbf y$. In the book ...
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27 views

How many samples are enough

I have objects with large number of attributes (about 60.000). Attributes are actually deviations of object part from model. I would like to cluster this objects, to get centroids that will represent ...
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1answer
63 views

Example of sample $X_1,X_2,\ldots,X_n$

In the book Statistical Inference by George Casella, it is written that An experimenter uses the information in a sample $X_1,X_2,\ldots,X_n$ to make inferences about an unknown parameter $\theta$. ...
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1answer
8 views

Test of two proportions from the same survey

I was wondering which test I should use for comparing two proportions from the same survey. Example: A survey of 1000 people ask two question. "Do you smoke everyday?" and "Do you drink alcohol ...
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3answers
98 views

Why take multiple samples from a population?

I'm fairly new to Econometrics, and I'm curious about, when trying to estimate the population parameter, why it is important to take multiple samples of the population, instead of just combining all ...
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1answer
51 views

Assessing a sample mean with a confidence interval vs a hypothesis test [closed]

I'm reading this pdf on statistics. I wanted to ask the difference between sections 3.5 and 4.2. In section 3.5 it is described how to compute, from a sample, an estimate of the mean with a ...
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2answers
26 views

Online Panel For Survey - Can It Be Representative?

I am thinking of using a company that has an online panel to recruit participants for a questionnaire study. Because the demographics (age, gender, region etc) of the entire population is known ...
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1answer
18 views

Are daily updated data a sample or a population?

I want to do some tests based on all historical data of a product updated on a daily basis. These data are not supposed to have any time trend associated with them just be pulled on different days. I ...
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44 views

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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12 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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1answer
45 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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1answer
45 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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14 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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34 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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1answer
90 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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31 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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22 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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37 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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48 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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1answer
32 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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15 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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17 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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22 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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25 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
42 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
309 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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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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2answers
88 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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53 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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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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123 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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87 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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3answers
132 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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69 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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0answers
44 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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1answer
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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30 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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24 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 ...