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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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Sample size (CI 95%)

I have two groups (treatment and placebo) and for each group I have the 95% CI mean calculated as per here. I want to do the same for calculating the 95% sample size as per table 11 of this paper: ...
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How to decide sample size for validation?

I have data having over 20000 rows. 1) I am going to use a tool to test how many error rates this tool will calculate in this data. 2) And then, I will randomly choose some data and check how many ...
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Favorite sequence in 10 flip tosses

I have the following question. Somebody likes to flip coins. In particular, this person is delighted to get a sequence HTTH. Assuming the person flipped coins 10 times, what is the probability that ...
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SPSS: Paired sample t-test (pre & post) for multiple groups with data in single datasheet [on hold]

I have two different groups with pre and post data for both in a single dataset. I want to do paired t-tests for group 1 comparing pre and post and also for group 2 pre and post. Is it possible to do ...
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How probable is it that I can gather a sample of 1600 people with crowdsourcing tools? [on hold]

I am considering using MTurk or Prolific for a survey. I want to gather data about 1600 people. These people will be working in the public sector. I am however not sure how likely it is that I am able ...
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Minimum Sample Size for M&A Event Study

as statistics beginner I was hoping you could help me with regards to the following problem: I wanna conduct an event study (analysing abnormal returns of share prices) to derive performance effects ...
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What does the distribution of samples from an MCMC method converge to without repeated samples?

Suppose I have an absolutely continuous distribution with density $f(x)$ and I use an mcmc sampler which has accept/reject step to sample from this distribution. In the final samples, there are some ...
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Conditional Probability Based on Sample When Population is Known

I have a count from each U.S. state of people that ride bikes. I want to know whether the count is larger or smaller than expected relevant to the population of each state (I also have the population ...
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Determine Sample Size [closed]

In determining sample size, how to analyze this problem. You plan to sample students from each of the following strata: Sophomores, N=1000; junior=N=500; Seniors, N=300. Answer the question below. ...
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Deciding on population vs. sample

I have been researching when to classify a dataset as population vs. sample for many hours now for a statistics project I am doing. I have a dataset of NFL combine data and one thing I need to clarify ...
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Calculating sample size for one 5-point likert item

I am trying to calculate the optimal sample size for a hypothetical experiment with the following: Treatment condition (n TBD) Control condition (n TBD) My dependent variable is an 'intent score' ...
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Evaluate Sample Representativeness of Dataset

I'm trying to check / evaluate how representative a sample is from a dataset. I'm interested in two things: Which sample best represents the original dataset Is the sample a "good enough" ...
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Web Based Survey Sampling method

I am doing a web based research with target audience as general public. I am a student and so due to limited resource, i basically did snowball sampling. I approached all those whom i knew, some ...
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Difference Between Notation of Two Sample Hypothesis Tests

Does this hypothesis test: H0: μd = 0 H1: μd ≠ 0 Represent the same as this test: H0: μ1 = μ2 H1: μ1 ≠ μ2 Since the first is asking if there is a difference between the true mean of the two ...
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How to create a scale combining normalized percentile scores to get an overall result

I am trying to work out a scale for assessing a person’s risk for a particular behavior (like rob a bank). The likelihood of this behavior occurring or not occurring will be based on scores for a ...
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Weighting cases if some population groups are missing in a sample

A usual way to weight cases in a sample for the $i$ category is taking its weight as $w_i$ = $P_i/p_i$, where $P_i$ is known proportion for that category in the population and $p_i$ – in the sample. ...
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what does that mean by saying “a sample having 2 (or more) observations”? does the observation mean possible outcome from an experiment?

Say, I am drawing balls. "drawing 2 balls from 3(labeled numbers from 1 to 3) with replacement" is an experiment. perform this experiment could result 9 possible outcomes. here is the list ...
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Location level a/b testing sample size

We are setting up experiments to measure impact on the city level. Customer in certain cities are treated and we have list of holdout cities with similar behavior. Measurement of lift of the ...
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Independent or Dependent sample

I am comparing whether Spot Gold prices and Gold ETF prices have the same performance. A spot price is the current price in the Precious Metals marketplace at which a given asset such as a security, ...
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R Calculate sample weights based on two socio-demographic variables and aggregate results

After conducting a short survey, I have collected the results in the form of a dataframe. This is a reproducible version of what the actual data frame looks like. ...
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Find significance between two group proportions

My question is the following: what statistical test would I use to compare the proportion of participants between two groups. For example, if in 2009, 20% of participants ( population was 55) to a ...
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Plotting groups of sample distributions as CDF with dispersion

Context I repeatedly run an experiment each repetition of which results in a sample of observations that I assume follow some distribution. (It is not important here what the distribution represents.)...
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29 views

Effective Sample Size for Weighted Samples

I have an MCMC sampler with weighted samples and I want to compute effective sample size at every step to determine sample degeneracy. I am using the following formula: $ESS = \frac{(\sum_{i=1}^N{w_i}...
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Sample Calculation of Morisita's Overlap Index

I am actually a biologist who has as question regarding how to apply the Morisita's Overlap Index. I have been told to compare two plant species by using this index and 3 other variables for each ...
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What is the cost of reconstructing a discrete probability distribution, from samples, within a given error?

I'm aware that there are several methods to estimate the probability distribution from samples (e.g. density estimation methods). However, I haven't been able to find the actual asymptotic costs of ...
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Why is unbiased estimation from a sample only possible for certain properties?

I was thinking about finding some monotonic measure of entropy of a sample from a continuous distribution (2D, btw), but couldn't think of any such without making assumptions. Why is it that one can ...
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Help with psychological research for my dissertation?

1) Is median split effective to divide participants in 2 groups considering their scores on a scale? I am using PECK scale (Personal experience checlist) and i need to divide participants into minimum ...
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Dealing with non-representative samples of a larger population

I'm seeking some advice about a project that I am working on. In this project, my colleagues and I are planning on collecting a sample that is intended to be representative of the national adult ...
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How do I report a Friedman Test when the sample violates the assumption: 'Group is a random sample from the population'?

How do I report a Friedman Test when the sample violates the assumption: 'Group is a random sample from the population'? My study involves a group of participants receiving an intervention and a ...
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Is it possible to estimate a population mean from a convenience sample?

I have data for which I can compute a sample mean. These samples are certainly not random. Is there any way to make an estimate of the population mean from a single biased sample?
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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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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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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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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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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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60 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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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 ...