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Questions tagged [sample-size]

This tag is very ambiguous. Use it when the question is about sample size and NONE of the following are more appropriate: [small-sample], [large-data], [power-analysis], [power], [underdetermined] or [unbalanced-classes].

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Type I and II errors accounted for by one equation?

On this website: https://clincalc.com/stats/samplesize.aspx both type I and II errors are accounted for by the one equation. Surely, because a type I error involves too much positive variance and a ...
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How to account for low sample size when computing performance?

I am interested in analyzing user performance at a per user level. Users have the opportunity to engage with an app by answering trivia questions and can choose how many questions they want to answer. ...
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Sample size calculation for parametric test, with large effect expected, small numbers. Should I use parametric or non parametric tests?

I am trying to figure out what would be the best way to analyze data from a randomized double blind trial we conducted. We sought to find if two dosages of a drug were effective for a severe symptom ...
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How small is too small to fit a reasonable long memory model?

When looking at papers about long memory they tend to analyze data sets whose length is in the thousands, see http://www.math.canterbury.ac.nz/~m.reale/pub/Reaetal2011.pdf for an example. My question ...
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1answer
30 views

Meaningful Sample Size

I have a set of 100 people each assigned to one of the four groups (very short, short, tall, and very tall). How many people's height do I have to measure to know the general distribution of people ...
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1answer
17 views

Minimum sample size to trust univariate cox regression

I have performed a univariate Cox proportional hazards regression for an admittedly miniscule group of 25 samples, and consequently received a certain p-value (significant) and an associated ...
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1answer
17 views

In AB test do the sample size calculations represent the minimum or maximum size required for measuring difference between the test and control

A quick question on the frequentest approach of sample size calculation. I recently came across this below note: The sample size required should be strictly enforced; if the power analysis shows ...
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1answer
22 views

Multinomial Logistic Regression: small groups

I am implementing a Multinomial Logistic Regression, but I am encountering the possible issue of having very small groups when I create a frequency table of the dependent variable Y and one of the ...
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1answer
34 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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20 views

Sample Size problem: Have done a trial/pilot, but how to proceed? [closed]

I have a problem in calculating sample size. I did do a small pilot experiment, so this is some sample data with the same structure: ...
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1answer
40 views

What is the requisite sample size for my study? [on hold]

Effect size = .2 Type I error = .05 Power = .80 3 predictors, one outcome variable My mentor suggested using a simple bivariate correlational model but I'm unsure.
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What is the relationship of skew and sample size on the sampling distribution?

I'm interested in the relationship between a distribution's skew and the sample size needed for the sampling distribution to be approximately normal. Let's assume the distribution is unimodal. In ...
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1answer
16 views

calculate sample size, differences between software

Currently I'm doing a power calculation using the pwr package. I thought it should be very simple, but I'm not sure if I'm doing it right. I use R to calculate the sample size. I checked my results ...
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What are appropriate statistic tests for top-down and bottom-up knockout experimental designs?

This concernes a two staged experiment on cell toxicality. A: Aim is to find the lowest concentration of the toxic agent 'CTA', that kills the target cells with at least 99% security. Use of lowest ...
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Dickey fuller to estimating other biases, intution needed

I have recently been working on replicating the Dickey-Fuller critical values i.e. generating the Dickey-Fuller test distribution. However, I would appreciate some intuition on this and some advice ...
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29 views

Calculating Sample Size for Cluster Randomized Trials with Person-level or Cluster-Level Outcomes

I have been looking for a formula to calculate the estimated sample size for a two-level cluster-randomized controlled trial with cluster-level outcome data. To my reading, several authors do not make ...
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13 views

Taking into account sample size

Let's assume that we have: 5 different conditions with an increasing concentration of a stress-causing agent. in each condition, 4 Growth curves and their area [under the curve] were generated from ...
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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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20 views

Quality Assurance: Sample Sizes & Margin of Error

I'm setting up quality assurance at my workplace. I am looking to examine individuals' performance on a sample of the population of an individual's pieces of work. Using a set of criteria, the auditor ...
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1answer
30 views

Sufficient sample size for skewed populations

I have measured 50000 individuals from a certain population, and 800 (~1.6%) of them have a certain characteristic (say green eyes). I can be pretty sure that this is an effect that is present in a ...
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9 views

Large discrepancy between MorePower and G*Power

I am planning the required number of subjects for a 2x2 analysis (one within-subject and one between-subject) to detect a medium-sized interaction effect ($\eta_p^2$ = 0.0588). As a first estimate, I ...
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2answers
136 views

MANOVA with variables from different datasets

I conducted several experiments where I have one underlying independent variable (tree species, IV). Each of these experiments gave me one dependent variable (DV), like bark pH, rugosity or the water-...
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32 views

Does the independence of samples in an experiment matter?

This is a bit complicated. I have a set of data of events happening in time, so my data looks like an array of time points at which an event happened. (Eg [2 45 50 51 60 79] in seconds) This data was ...
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16 views

Offset in NB model produces contradictory results to original data

My (example) data frame is rather simple. I would like to know if there is a difference in numbers between the factors (n=2) within variable X. ...
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51 views

How to reduce sample size in predictive model?

I am working on a regression model, which purpose is solely to predict new data. My training dataset contains around 200 measurements and with a best subset regression i was able to find good models ...
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17 views

Estimate the sample size needed for a chi-square test comparing four percentages

I am trying to compare the percentage of males among four countries using Chi-square test. From a previous similar study, I know that the percentage of males in these four countries are 0, 10%, 30%, ...
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25 views

Sample size determination for analysis with several multiple regressions

In a proposed analysis that involves several multiple regressions, how can we determine the required sample size? If, for example, we can tolerate a type I error rate of 5% ($\alpha$ = 0.05) and a ...
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7 views

Within Subjects Power Analysis

I'm troubling over the role of number of observations in a within subjects design on power. Let's say I have a 2x2, or even a single factor, completely within subjects design. A power analysis might ...
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1answer
44 views

What are the problems if in a AB test the control group is not big enough?

I've been asked to analyze some data but I'm quite new in statistic. I want to compare the means of a continuous parameter in two independent population A and B: A can be seen as the treatment group ...
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58 views

Repeated measures ANOVA sample size calculation using R

I'm trying to conduct a sample size calculation for a repeated measures ANOVA. The study will involve taking 10 measurements from participants. Prior to each measurement, participants will be ...
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3answers
43 views

Eliminating variation in sample size for A/B tests

Firstly, I'll apologise for my limited understanding on this topic. Let's say I am running an A/B test with a pool of 20,000 prospects and I split them 50/50 into A and B. The problem is, the ...
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Can cross-validation+bootstrapping be used to estimate the required sample size to achieve a “narrow” estimate of prediction accuracy

I am aware that the question may not seem very clear at first sight. So let me elaborate on this. I have certain data (let's call it "exploratory dataset") on which I have performed survival analysis ...
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22 views

Sample size calculation for survival analysis in retrospective analysis?

I need some reference to the following question: I need some rules of a thump for a retrospective multivariate survival analysis. We are looking at cases that got cancer of urinary bladder, prostate, ...
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26 views

Determining sample size for a binomial distribution for a given confidence interval when the probability is close to 0 or 1

I've found formulas for determining sample size for when the probability isn't close to 0 to 1. However for the case when it is close to 0 or 1 I'm unable to find any formulas.
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Pearson's r, Point Biserial Correlation, and Sample Size effects

I am currently trying to test a model for cross-cultural adaption and need to do a simple correlation analysis between the predictor variables (language ability, adaptive motivation, degree of culture ...
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1answer
35 views

Sample size for estimating success probability of a Bernoulli process

Suppose an AI player in a game can either win or lose. I wish to estimate the win ratio of this player. My question is, how many samples (games) needed in order to get an error smaller than 1%? A ...
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27 views

Cohort Study Sample Size and Multiple Comparisons

I'm designing an epidemiological retrospective cohort study with a large number of exposures and outcomes, and I'm trying to figure out how many subjects I'll need in order to run all my analyses. The ...
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17 views

How to determine sample size for factorial experiment (2^3)

I am designing a factorial experiment with two independent variables at three levels (2^3). How do I determine how many samples to collect and how to allocate them. Further, after reviewing the ...
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55 views

Convince me that AIC can't be used to compare models with different sample sizes

Conventional statistical wisdom says we cannot compare AIC (or other information criteria predictive sample statistics) when the sample sizes for the compared models are different (See here for ...
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1answer
43 views

Why is the false acceptance probability not improving with increasing sample size?

We have a normal distribution with zero mean. We have two hypotheses for the variance $\sigma^2$: $$H_0: \sigma^2=\sigma_0^2$$ $$H_1: \sigma^2=\sigma_1^2$$ We make $n$ independent observations $X_1, ...
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How to Calculate Sample Size for a two samples Welch's t test given a wanted power for an expeted effect size (without R)?

I have found no answer on web search engines for that. And even though I was able to find here some answers on how to calculate the power of a Welch's t-test here, they were expressed in R code. As I ...
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29 views

Sample size and standard errors in OLS estimation

The standard errors of the estimated parameters from OLS estimation strongly depend on the sample size (n). Indeed, the standard errors tend to decrease when the sample size gets larger (ceteris ...
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30 views

Estimate unknown sum of iid random variables

Let $X_1, X_2, \dots$ be a sequence of independent and identically distributed discrete random variables with common mass function $f_X(x)$ defined for when $x \in \{0,1,\dots,N\}$ and $N$ is known. ...
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1answer
39 views

“effect size is independent of sample size” really?

I keep reading "effect size is independent of sample size" on the interwebs. Don't get me wrong, I get the practical vs statistical significance considerations. What I don't get is that; -power,...
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1answer
54 views

How big should be a sample size?

Question: Assuming the population standard deviation σ = 3, how large should a sample be to estimate the population mean µ with a margin of error not exceeding 0.5? My answer: SE<= 0.5=3/√n ---> ...
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19 views

Sample Size Adjusted Metric for Calibration Curve

I'm creating a model that provides a predicted probability of an event happening. I am using calibration curves that plot predicted probability (x-axis) versus the actual event frequency (y-axis). I ...
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0answers
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how to compute a minimal sample with some prior information?

Suppose N = 30, 000 students in total and a SRSWOR of size n will be taken from the population. And we want the proportion estimator ^p to achieve the precision with tolerance level e = 0.03, risk α = ...
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1answer
20 views

Comparison of means from different sample sizes

I have a data set which contains avg profit and the number of samples for each data point, no more information. I'd like to compare the data points and decide which one to focus on more. However, I'm ...
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1answer
83 views

How can you compute sample size for a linear mixed model? G*Power only does repeated measures ANOVA

I read everywhere that repeated measures ANOVA is inferior to mixed modelling (since it doesn't handle missing data as well and relies on sphericity assumption). G*Power doesn't tell you how to ...
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1answer
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Is there a systematic reason why a model trained on a subset of data does better out-of-sample than the same model trained on the full dataset?

I trained a linear regression model using 3000 data points. (OLS regression, no regularization.) Then I trained another model with the same predictors (about 25), but with a subset ($n=700$) of the ...