# 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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### Sample size calculation for linear regression model with random intercept

I am trying to calculate the sample size for a mixed linear regression model. The dependent variable is continuous and the model includes 2 further continuous variables. The random intercept is based ...
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### Sample size calculation for simple logistic regression. What's wrong with my code?

I want to learn how to calculate sample sizes for logistic regressions. Therefore, I want to reproduce the first example of https://www2.ccrb.cuhk.edu.hk/stat/epistudies/reg3.htm with P_1=0.4 (...
14 views

### sample size calculation for testing classifiers

Normally when determining the sample size per group to see if two groups are different in their mean a power analysis (e.g. here) is used followed by a t-test (and p-value). I was wondering if there ...
11 views

### moderate size of the data sample [closed]

It is often that the authors of papers in AI, ML and Statistics write that their methods are proved to perform good for "moderate sample sizes". I saw this statement in very high ranking ...
5 views

### Translation of between-subject sample sizes to within-subject sample sizes

The following formula can be used to translate the sample size needed from one way between-designs (NB) to sample sizes needed in one way within-designs (NW): NW = NB(1 − ρ)/number of data points per ...
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### Formula for sample size for hypothesis test for difference in proportions confusion

For a hypothesis test for difference in proportions: Source A(Some Stanford professor): The sample size for both groups is $$\frac{2\bar{p}(1-\bar{p})(Z_\beta+Z_{\alpha/2})^2}{(p_1-p_2)^2}$$ \bar{p}=...
26 views

### How to appropriately reduce data size or take a representative sample from it?

I have a spreadsheet file with around 150,000 pairs (x,y). I wish to work with a smaller file, i.e., with less data, so my exploratory analysis is faster. What is the appropriate way of resampling, or ...
27 views

### Mann-Whitney test for unequal sample sizes

I want to run a Mann-Whitney test. But I got to know to know that for sample more than 20 we need to apply a different formula. My data sample is as follows. Group A contains data of 4 people and ...
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### Can trials have a differing number of samples when running PCA ? Why not?

Can somebody confirm that the number of "samples for each trial" doesn't matter(i guess that's right the language) for PCA. The case at hand is this: i have 5 sets of 3-dimensional ...
71 views

### Sample size for Pearson's chi-square test of independence

I'm trying to do a $\chi^2$ test of independence between two variables. The problem I have is that I'm struggling with the sample size for the test. I always end up with some cells that have 0 samples....
31 views

### Training data size requirements for imbalanced class classification

Our team is planning to start data collection for an imbalanced binary classification task. One in 30 cases is positive class and the rest 29 of the 30 cases are negative class. We have around 20 ...
23 views

### Is the p-value dependent on n in case of paired student t-test?

I have a dataset where we believe there are a bunch of infected and uninfected subjects (total being 15). There are two ways to categorise these subjects into infected/ uninfected: 1. categorise 10 ...
24 views

### How to compare model fits between datasets of different sizes?

A measure like mean square error appears to tolerate some variation in dataset size but, for example, a two-parameter model is still likely to produce a great (yet meaningless) fit to any dataset with ...
26 views

### A tail bound for an unknown distribution via sampling

I know that many results exist for making an argument about the tail of a distribution, i.e., for a random variable $X$, one can find a bound $\epsilon$ such that $\Pr[X \geq a]<\epsilon$. Some ...
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### marketing hypothesis test sample size calculation

I am trying to design a coupon promotion test to measure the increase in the volume of orders from promotion versus no promotion. To do so, I want to calculate the pre-group sample size required to ...
16 views

### Sample Size Calculation - Two Gamma Distributed Mean

I have a similar question to Sample Size Calculation - Two Independent Means, in my case, I am measuring the number of orders our customer make which follows a gamma distribution I believe. How could ...
2k views

### Given two samples that have the same mean, standard deviation, and N: are the values in each sample identical?

If not, are there any restrictions that would need to be imposed to ensure that the values of the two samples would be identical? I apologize in advance if this is such a basic question.
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### Using Welch's t-test for samples of very different sizes

If I have two groups, one with a sample size of, say, 700,000 observations and another with 10,000 observations and I want to test the difference between the means of the two groups, what would be the ...
26 views

### Sample size, confounding, bias

I have doubts. I use data on electricity consumption per capita (per year) from 1960-2014. The sample size in this case is N = 55 for the whole world, as well for individual regions and countries. ...
26 views

### What is a sufficient sample size for a logisitic multilevel (three-level) analysis?

I have an exploratory research question for which I use a repeated measure design with 3 levels: level 1 = 3 measurement occasions per day level 2 = day level 3 = participan To keep the effort for ...
33 views

### Sample size vs F1-score, which is more important (small sample size)

I work in a filed were there are many publications based on classifiers trained on small samples sizes (but large amount of features). In most cases the sample size can only be increased by a few ...
70 views

### Test if population sizes are statistically different?

I'm running an A/B test to see if the improved website layout increases revenue. First, I would like to check if the sizes of the control and experiment groups are statistically different. I have data ...
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### How to calculate number of participants and stimuli for experiment to reach significance?

I am running an experiment to determine the best performing of 5 systems, labeled A-E. I plan on running pairwise comparisons, e.g. is A better than B, A vs C, etc.? For the sake of argument, we can ...
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### Interpretation of results from ssizeRNA power analysis

I have around 200 subjects and I would like to check the power for 90 of those subjects. It is a case control study. I did this: ...
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### Testing for normality with small sample sizes in order to use t-test [duplicate]

I run into a conundrum when determining whether a small sample is appropriate for a t-test. I know that if I meet the assumptions, a t-test produces approximately correct inference with any sample ...
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### Advice on how to answer the “how large of a sample size do we need to show results” question to non-quant people in a business setting

Not sure if this question is too vague, but I'll give it a shot. I've received many questions from non-quantitative colleagues along the lines of "what sample size do we need to trust these ...
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### Independent variables minimum counts for logistic regression

I have about 100 samples collected to know the knowledge status of people and it's distributes almost 50 50. The problem is some of my indipendent variables while making 2x2 the cell value is very ...
128 views

### Calculating Sample Size for Confidence Interval of Given Level and Margin of Error

I would like to calculate my ideal sample using the Qualtrics calculator: https://www.qualtrics.com/de/erlebnismanagement/marktforschung/stichprobenrechner/ For this, I need a confidence level and a ...
21 views

### How to determine data size is statistically efficient?

I have a question about the data size for probability of default model. For each consumer, I have a binary bit to indicate whether the client goes default or not (1 is default and 0 is current). And I ...
19 views

### Minimum random sample with at least one persson that is infected with coronavirus

How large of a crowd will guarantee that at least one person is currently infected with coronavirus? For the sake of argument assume a "crowd" is approximated by a random sample. More ...
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### Power of two-sample test of binomial proportions

Suppose that I have info about a sample, and In one University, we have 70% females in the population and 30% males. In another University, the numbers are interchanged and 30% are females and 70% are ...
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### Select a sample size form the infinite population

I have a list of every store chain in the US with at least 100 locations in the US. a) What number of those do I have to pick in order to have a representative sample of the number of locations across ...
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### Central limit theorem - num random variables vs. sample size?

Does the Central Limit Theorem require the number of random variables to increase to a sufficiently large number or the number of samples of each random variable to increase to a sufficiently large ...
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### Controlling for a variable with unequal sample size

I'm dealing with a Poisson regression model for count data. My DV is the number of Covid infections in a particular city. My explanatory variables are both categorical and continuous. One of them is ...
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### FDR control on many t-tests performed on different sample size

I'm a PhD student working in bioinformatics, on genome sequencing data. My knowledge comes to its limits here on hypothesis testing and FDR-control/multiple-comparisons. Any help would be truly ...
23 views

### correcting for small sample sizes

I have been toying with some data relating employment outcomes to choice of college major (which I got from a FiveThirtyEight Git repository). I have included a scatter plot where each point ...
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### Does sample size affect choice between fixed and random effect

I am analyzing data as given in this question: Should "City" be a fixed or a random effect variable? Here it is debatable whether "City" is to be kept as fixed effect or random ...
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### Sample size analysis for retrospective analysis of survey data

I have data that were collected on childhood injuries for 1 year at clinics in certain US states. The data were then aggregated, with weights and strata to be nationally representative. This is ...
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### What is best practice for study design and sample size calculation for PCA?

I am trying to understand existing practices for study design when the intended analysis includes PCA. General practice would be useful to understand but the most interesting would be designs for ...
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### Sample size calc for logistic regression with continuous variable * binary variable

I would like to calculate the adequate sample size for the following experiment: There will be 2 groups: a control group ($T=0$) and treatment group ($T=1$). Each group has a continuous covariate $X$. ...
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### Approximately how many data do we need to train a artificial neural network with 2000 parameters?

My approach is to think about ANN like a common statistical model. 2000 data for 2000 parameter is clearly not enough. However, if we got 10k data points then the training result might start to become ...
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### How to interpret P-value result in light of P-value used for sample size calculation

A study is planned comparing effects of 2 drugs. Sample size is calculated for power of 0.8 and alpha of 0.01 After study is completed, the results show that there is a difference between 2 groups and ...
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### What is the minimum sample-size required to be confident that half of American adults have eaten ice-cream at least once in their life?

Suppose that you conduct a survey in which you ask American adults if they have eaten ice-cream at least once in the past. What is the minimum sample size required for you to be at least 90% confident ...
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### Is result of this simplified formula for sample size for one group or for both groups?

I see there is a simplified formula for calculation of sample size for comparison of proportions given on this page. The formula is: ...
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### ANOVA with groups having different sample sizes

I have 3 groups Group 1 with sample size ($n_1$) = 54 Group 2 with sample size ($n_2$)= 87 Group 3 with sample size ($n_3$) = 409 Can I carry one way group ANOVA? Also, can I include this ...
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### Power calculation for a one-stage, single arm trial with continuous primary outcome

An early-stage single-arm clinical trial is being planned to evaluate the efficacy and safety of treatment for a bacterial infection. The primary outcome is binary - proportion with >0.5 log10 ...
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### Statistical comparison for large sample sizes (n>1000)

I am comparing the drug exposures across two different groups, consisting of 1000 simulated drug exposures per group. Drug exposures are continuous variables following a normal distribution. I want to ...
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### Does higher degrees of freedom reduce variance in linear regression?

I'm trying to figure out why higher degrees of freedom $(n-1-k)$ in a linear regression is "better". I can't see how higher df would automatically result in lower $MSE$, since every new df (...