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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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28 views

Power and sample size calculations for unpaired ROC curves

I would like to perform power and sample size calculations for comparison of unpaired receiver-operating characteristic (ROC) curves. I have tried using the power.roc.test function from pROC package ...
23 views

Am I understanding and applying Sample Size correctly?

I'm trying to see if I'm applying the Sample Size concept correctly to my problem. I have a survey where 20,000 people replied for a population size of 4,000,000. The question asked which product ...
9 views

how to understand an unit of analysis

I came a cross a definition which I cannot understand the logic. is there a way to explain what is the problem ? a longitudinal design for an intervention study in 10 participants where the ...
9 views

Back-calculation of the minimum sample size for an mechanical experiment [closed]

I want to back-calculate the minimum sample size for an experiment. I have a known mean and standard variance of a statistical population. From the statistical population I chose two samples with ...
21 views

How many experiments to run (sample-size) if I know I am going to feed them to a non-parametric regression?

I have 2 input variables, $X_1$ and $X_2$ that affect output variable $Y$. I can run experiments where I modify the inputs and measure what happens to the output. Now, if $X_1$ and $X_2$ were binary, ...
17 views

Find the minimum sample size to test for a normal distribution and 1-way ANOVA

I have been heuristically choosing sample sizes and would like to find a more quantitative method. For each group of my data I want to verify that they are normally distributed. Then I want to check ...
18 views

Determining sample size for chi squared

I'm currently writing a project proposal in which i've been told i need to estimate the sample size i require. Im planning to look at the effect of culture time (split into three groups) on IVF ...
56 views

Required sample size in internal audit

In applied literature about the required sample size such as "Sampling for effective internal auditing" we find formulas for the required sample size to detect a proportion of a feature or an error ...
76 views

Behaviour of Welch's t-test with unequal group sizes

It seems that in some cases Welch's t-test can give inflated p-values with imbalanced group sizes. For example, consider the following simulation of unequal group sizes sampled from the same Gaussian ...
35 views

Is it scientifically feasible to compare two samples of different sizes, while values in each sample are average numbers? [closed]

I want to compare result from my protein docking experiments to various protein structures of the same protein. I have two samples and in Sample 1, I have ...
32 views

Determining sample size for Structural Equation Model with R

I want to run and experiment to test the validity of a theoretical model. I have the structural and measurement model, but do not have previous data on any of the parameters. Is there a way I can find ...
67 views

What is the correct effective sample size (ESS) calculation?

I wish to compute the effective sample size (ESS) for a posterior sample of size $M$. I have looked at several documentations (e.g. WinBUGS p11; Stan sec 15.4) and several other Stack Exchange ...
33 views

Selecting a proper sample from a dataset for a hypothesis test

I have a dataset of about 800k subjects and within that dataset 7025 subjects have either disease A or disease B. I'd like to test the hypothesis (chi squared test) that subjects with disease A are ...
41 views

Can results for model selection with AIC be interpretable at the population level?

AIC results for model selection are dependent on the sample size. For example if I make this model with a sample size n=100: ...
15 views

Does the sample size calculation depend on the type of distribution?

For example, will the minimum sample size for a 95% confidence interval and 2% margin of error be different for a normal, binomial, Poisson, Geometric, Weibul, etc distribution?
44 views

Sample size and variance

A random sample of size n1 = 16 is selected from a normal population with a mean of 75 and a standard deviation of 8. A second random sample of size n2 = 9 is taken from another normal population with ...
7 views

Pre-hoc methods to determine sample size based on known number of features and classes

What are some pre-hoc methods that allow me to determine (or roughly estimate) sample size based on the known number of features and classes? I have found this article: Optimal number of features as ...
43 views

Calculated sample size and calculated p-value in two independent t test [closed]

I would like to know the relationship between sample size and p-value. When comparing two independent means. Sample size calculation 1) Expected difference between two means: 2.8 2) Expected ...
156 views

Sample size determination using historical data and simulation

I am interested in the legitimacy and classification of the following approach to sample size determination. This question is inspired by “There is only one test!” by Allen Downey and “Statistics ...
18 views

how to determine sample size for continuous metric

many online sample size calculator like http://www.evanmiller.org/ab-testing/sample-size.html only have sample size calculation for discrete metric(like conversion rate) how to calculate sample size ...
26 views

Increasing the sample size for ttest without additional observations

I am currently handling some satistical data but my sample size is too small fot testing and my suppervisor suggested me the following idea: Consider 2 samples x, y and we want to compare the ...
34 views

Are a distribution's higher-order features harder to estimate?

In what sense, if any, are a distribution's higher-order features (e.g., moments, cumulants) harder to estimate than its lower-order features, for at least some distributional families? For example, ...
11 views

Clarification on Central Limit Theorem (Sample Mean vs. Sample Distribution)

I know the CLT says that as sample size (n) increases, the distribution of the sample mean has a mean that approaches the population mean and the variance of those means approaches (σ^2/n). The way I ...
19 views

Sample size for n-th percentile order statistic with no approximation for non normal distribution [duplicate]

Given we have population (N) say 1e9, how to estimate sample size proper sample size for obtaining valid n-th (say 99) percentile value with small margin of error ? can we use this calculation This ...
11 views

Validate Z-score Formula

I need need help validating a formula for a z-score. I have a book that I enjoy but in my re-read of the materials, I have found that the author has made some fundamental errors in their writing. So, ...
34 views

I am not understanding this example of Chebychev Inequality?

I am trying to teach myself statistics and am reading DeGroot's book. Anyways, I'm in Chebychev's Inequality and am confused by this example: I understand the second part about if we know the ...
17 views

Calculate proper number of elements in a sample

Suppose that I own several convenience stores across the U.S. and I want to infer the share of market for different brands by just analyzing their sell behavior in my stores (ex. I might infer that ...
29 views

Confidence interval for the mean

If we want to create a confidence interval to estimate the mean of a specific population and we want the margin of error not to exceed $10$ at confidence level of $90\%$ given that some study suggests ...
16 views

Appropriate sample size for model validation with RMSE errors

I have been looking over the internet for a way to determine the appropriate sample size for a validation experiment that validates the RMSE results from a deep learning (CNN) model. The network was ...
29 views

How to determine whether a validation study produces acceptable results?

I have a method developed to predict results of a signal that outputs an root mean squared error (RMSE) for each subject. Combining all 40 subjects (2 samples for each subject), I get a mean RMSE of 5....
35 views

Is my sample size vaild

I am conducting a survey. Based on my calculation, I need a sample size of 300. However, I could only obtain 120 people to do my survey. what can I quote to justify the validity of my survey? CLT > 30?...
33 views

ROC-style curves for calculating sample size, power, alpha, and effect size

I found an awesome R package called pwr that does all sorts of calculations about sample sizes, power, effect sizes, and so on, and I've been playing. I have a ...
10 views

Samle size calculation for paired comparative diagnostic accuracy study

I would like to estimate an appropriate sample size for a medical imaging study. I prefer to use R. A standard thest testS will be compared to a modified standard ...
27 views

Question about Bayesian Polling

A professor in the United States reads a headline stating that only 36% of Americans have ever been outside the U.S. She believes the headline to be true and would like to know whether the 30 pupils ...
41 views

Can Kruskal-Wallis test be used in groups of different size?

I am trying to compare Likert-scale answers to a survey applied in 3 different cities: A, B and C. I arbitrarily chose twice as many respondents from A, for a total of 500 answered questionnaires in ...
16 views

Pooling F-values? Effect sizes and sample size estimations

Im struggling with the power in general.. I need assistance with how to calculate sample size with confidence intervals as to be able to conclude that the sample of the present study is within XX % ...
87 views

Central limit theorem and normal distribution confusion

So I'm trying to study for a test and I'm stuck on two textbook questions. I'm having trouble grasping the concept of sampling distributions and when to apply certain rules/when to categorize a ...
9 views

Power and sample size estimations, how to standardize and compare to previous research. MLR or Correlation for effect size?

Ok, there are a couple of questions here to be honest, Background: I am assessing if thinking,(INFP (Likert scale, 4 subscales) and CT (Likert, two subscales) predict (other-rated) perceptions of ...
17 views

R power.prop.test for two samples with different proportions

I am trying to modify power.prop.test is R to adapt for cases where n1 and n2 (two sample sizes) are not equal. That is, they can not be given by one constant n. The equation in R for n1 = n2 = n ...
21 views

High frequency FX data and sample size - possible autocorrelation

I have data for EUR/USD at 1 minute intervals for 2003-2018 (approx 5.86million data points) I have read papers that say that "high frequency data" suffers from "extremely high negative ...
41 views

nonparametric sample size calculation

I am running into conflicting information regarding a running a sample size calculation for a nonparametric dataset. I will be collected data from a medical procedure that gives pressure readings ...
26 views

Power Calculations for 3 arm clustered randomised trial

I need to do power calculations for a 3 arm trial (to determine minimum detectable effect size, given the alpha, power, sample size etc). I found the R package Three.Arm.Trials, however I was ...
34 views

How to choose at what sample size standard deviation becomes reliable for my purposes?

I'm calculating standard deviation for a normally distributed variable. I'm receiving data samples online, and I've noticed that right after the start (for a small sample size) standard deviation is ...
27 views

sample size for normal distribution

i have a small set of data. I'm sure that their distribution is normal, with standard deviation $\sigma=10$. I'm interested in the mean value, $\mu$ and its uncertainty. Which is the minimum sample ...
22 views

Chi square test between samples with very different size

I am to estimate the chi square between two samples of size N and M, where in general N << M (e.g. N=100,000 M=10,000,000). In turn, this affects the uncertainty of each sample. I wonder if ...
15 views

Importance and consequences of the sample analysis for the Bland/Altmann plot

It is my first post here, please let me know if it is unclear or not enough documented. To compare two measurement methods (ECG), I am using the Bland Altmann plot method. As I only have 28 ...
88 views

Does it make sense to do Cross Validation with a Small Sample?

Sorry for the novice question, very new to CV. I have a set with 16 samples and 250 predictors. I'm being asked to perform CV on the set. In the examples I've looked at, you create training and ...
189 views

What is a reasonable sample size for median statistics?

I am asking this question because of a recent question on Skeptics.SE and a 2015 study by Duke University and the Federal Reserve Bank of Boston. This question is based on the study. In a Boston ...