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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Clinical trial when there is no raw data

I'm conducting a clinical trial with a treatment group and a placebo group. Based on the raw data, I calculated the needed sample size for each (they should be the same) and used ANCOVA to confirm ...
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Calculate sample size for multiple treatments vs control, given the proportion mix of treatments

I want to know what my sample sizes should be for each of my treatments and control, given a proportion mix between the groups. For example, let’s say I have 3 treatments (A, B, C) and 1 control (D). ...
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Sample size calculation for Cox regression with time-varying exposures

I'm involved in the design of a longitudinal observational study investigating a relationship between the use of a drug and a binary outcome. Participants are enrolled when at risk of the outcome, ...
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Power / sample size estimation for chi-square test with continuity correction in R

1._Some authors mention that they estimate sample size for chi-square test with continuity correction. For instance: Sample-size calculation is based on Pearson's Chi-square test with a two-sided ...
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Should you clean your data after or before selecting a sample?

Assuming a 500k dataset. For statistical modeling purposes (selecting up to 10% of 500k as a sample). Should I clean the 500k dataset first before selecting a sample or select the sample first and ...
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How to determine sample size when performing indirect sampling?

Problem Summary I want to know the minimum sample size needed for a given confidence level and margin of error when performing indirect sampling where samples from the two populations are not one-to-...
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Number of confidence intervals for Binomial Distribution

Consider the random variable $X$ to denote the event that the confidence interval cover the unknown parameter or not. Thus, X will follow the Bernoulli distribution with a parameter $θ$, i.e. $X~Be(θ)$...
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Propensity score matching sample size

I am considering doing a propensity score matching to evaluate the effectiveness of a intervention. However, i only have 193 cases in my treatment group. I have a lot in control group. My outcome is a ...
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How to deal with ragged power curve

I am exploring various methods for sample size calculation and power analysis from binomial data, and frequently coming up against ragged power curves that go up and down as sample size increases. I ...
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Sample size and power for an F-test with more than 2 samples

There is a known formula for calculating the minimum sample size for t-test: $$n = \frac{\sigma^2 z^2}{m^2}$$ where $\sigma$ is the (expected) standard deviation in the population, $m$ the margin or ...
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Sample size for interaction term in HLM

I am running a hierarchical ordinal regression model with 41 subjects evaluated at 5-time points each. Besides a single level-1 time-varying covariate, I only have two other explanatory variables - ...
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determining the sample size for quality test

It has been a long time since I did statistics in uni and I have a "simple problem" that I need solving. I need to determin for a sample size for a limited population of documents ( lets say ...
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3 votes
1 answer
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Comparing percentages from different sample sizes

We have questions about how to run statistical tests for comparing percentages derived from very different sample sizes. Specifically, we would like to compare the % of wildtype vs knockout cells that ...
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How to Ensure Saturation Using Grounded Theory?

In quantitative causal inference, we do power analysis to determine the minimum sample size to achieve (1 - $\beta$) statistical power of our hypothesis test with a specific $\alpha$ statistical ...
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Sufficient sample size in multinomial Machine Learning problem

I have a small sample with three unbalanced classes (class1 and class2 ~ N=60, class3 ~ N=200) and behavioral data (clinical data such as alcohol consumption). I have read a lot about the question of ...
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6 answers
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Why does Machine Learning need a lot of data while one can do statistical inference with a small set of data?

I am wondering why Machine Learning needs a lot of data compared to statistical inference. In statistics, we can use a small amount of data for a statistical inference but in Machine Learning, ...
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When the anticipated sample size is not reached in a clinical trial

How to justify precisely a situation where the expected sample size is not reached? For example, the sample size for our study protocol was determined on the basis of a fixed statistical power of 80%. ...
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2 votes
1 answer
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What happens statistically, if you create more observations by measuring more aspects of the same observational unit

Let's say that I want to measure the effect of a treatment on the performance of a firm. However my sample is very small. Let's say 10 firms. It is not possible to observe more firms. All these firms ...
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How to deal with groups of different sample sizes in phylogenetic GLMs (PGLS)?

I am currently working on a project that aims to characterise in R on a pool of 500 bird species the traits that may be at the origin of their introduction outside their natural habitat and thus ...
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The minimum number of sample size for two-way MANOVA and unequal sample sizes

I have 2 categorical IVs(2 levels in each variable) and 3 continuous DVs. One IV is teaching approach and the other one is education (a moderator). I'm going to examine the effect of the 2 IVs on DVs ...
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Required sample size of CFA using power analysis from semPower

I want to conduct a confirmatory factor analysis (CFA) for a model with 4 latent variables and 60 indicator variables (15 per factor, uncorrelated factors, hence 1,710 degrees of freedom, that is, ...
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Comparing the width of two percentile intervals

Suppose I calculate 99% percentile intervals for two different sample sizes, for example N=10 and N=1000 by doing the following: I take 1000 samples of size N=10 from the population (not bootstrapping)...
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Is my sample sufficient for PCA?

I’m working on a project for my stats class and I’m wondering if my sample size is sufficient for PCA; I keep seeing mixed recommendations so I figured I’d ask. My sample size is 50 (unit of analysis ...
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Phillip-Perron test - sample size requirement?

I understand that both Phillips-Perron and Augmented Dickey Fuller tests are for the presence of a unit root in a time series. It is my understanding that these test conduct those tests differently, ...
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3 votes
1 answer
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Sample proportion vs mean proportion for sample size estimation

Context I would like to estimate the sample size needed for an experiment. I’m testing a feature on a website and would like to detect a significant change between different variants . One control and ...
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2 votes
1 answer
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Sample size calculation for precision at $k$: a/b-testing a recommender system

I would like to conduct an online experiment to compare two different versions of a recommender system. The system returns a list of $r$ ranked recommendations. I would like to evaluate the ...
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Expected sample size for sequential t-test

I have a 2 group sequential one-sided t-test setting. $1-\beta = 90\%$, $\alpha = 5\%$. Null hypothesis is $\mu_1=\mu_2=1800$. Alternative hypothesis is: $\mu_1\geq\mu_2$ Plug-in estimate of $\sigma$ ...
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Minimum sample size of an observation in an unbalanced panel

I created an unbalanced panel from my raw data with several million cases. In this panel, each observation represents one city in one month. For some cities and months, only 5 cases are available as a ...
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4 votes
1 answer
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Adaptive LASSO, confidence interval and sample size

I have almost no experience with math or stat, but I am trying to run an Adaptive LASSO on a continuous outcome with around 200 cases and a list of around 19 variables. Some of these variables have 3 ...
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Estimate sample size from a variable population

Context: I want to measure accuracy, precision, and recall for individual raters. Each rater completes a variable amount of labels, for ex. rater A may complete 500 in a given time period while rater ...
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Power estimation and analysis for multiple 3x3 count tables

In my design, each subject produces a 3x3 contingency table.So I have a table of counts of how many times a subject responded X Y Z in condition A, B or C. All the columns sum up to 50 (num of trials ...
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Is the size of a bootstrapped sample the same size as the original set? [duplicate]

I'm currently trying to understand the Bootstrap method. I have a rather simple question. Say I have my original set S of size N and wish to create B bootstrapped samples of size R. Hastie et al. ...
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Is it true that a larger, representative dataset is always better to use than a smaller, representative dataset?

By "representative" I mean that the data in the dataset faithfully reflects the "underlying signal" a model is trying to tap in to. Is it always true that, as long as increasing ...
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Can parallel designs be considered the "gold-standard" for RCTs

Statistically speaking, are parallel designs the "gold-standard" for RCTs? I mean statistically in opposition to financial, ethical or operational aspects. The only drawback I see for (...
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How to find an optimal sample size (or range) based on sampling errors?

Intro to problem Increasing the sample size can be very costly in terms of time and money. However, in experiments where we measure proportions within a sample, errors associated with the sample size ...
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How to do conclude a treatment works when sample size is small with large STD and small effective value

I have a data which population is 3000; mean is 16; stdev is 44; I want to have a test case to check if the mean can be improved to 16.5 or not. After the calculation, I was told the required sample ...
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Comparing two uneven datasets, both of which were sampled in different ways

Dataset X is small (n=100). It was sampled based on a specific variable. Say, it took data based on 3 countries. Something like this: ...
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1 vote
1 answer
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formula for sample size calculation one sample t-test

This question might be really easy to answer, but I am not able to figure it out. For a project, I calculate sample sizes for a one sample t-test using the pwr ...
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1 answer
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Using s to estimate $\sigma$ when finding the sample size in confidence interval questions

I am trying to learn sample confidence interval for $\mu$ , in this topic , there is a subtopic which is finding the sample size. I know that if $\sigma$ is given (standard deviation of population) , ...
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How to determine sample size for equivalence testing in a bayesian framework?

I am planning an experiment to test whether a variable of interest (segmentTime_taskA) determined in a task A is equivalent to the same variable determined in a task B (segmentTime_taskB). In other ...
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1 vote
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How to get the standard deviation when summing down a category with multiple independent observations?

I am not sure how to handle calculating the standard deviation in my situation. Four researchers (i.e., R1, R2, R3, and R4) are taking independent measurements of the same variable—the time that a ...
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Problem with sample size: total number with mean or individual cohorts with mean?

I have a climbing assay where I use cohorts of multiple flies and calculate a performance index based on their climbing speed. I do this 15 times and then take a mean for the cohort. This has been ...
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Does the variance of the regression coefficients in simple linear regression always decrease when sample size increases?

As the title says, I am wondering if the variance of the regression coefficients (intercept and coefficient of x) always decreases with an increased sample size. I managed to figure out that the ...
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1 vote
2 answers
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Median Survival Time for Clinical Trials

I have a Clinical Trial where I'll be comparing a drug vs placebo. Then I intend to run a Log-rank test on it. Now for the sample size calculations, I would be requiring the hazard ratio and the ...
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4 votes
4 answers
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How can I reduce a very large sample size for statistical significance (sampling methods)? [duplicate]

In my biological study, I have around 14000 independent samples, and I study the evolution of a response variable over time. I have three groups to study. Thus, I have two factors: factor "Group&...
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Sample size estimation for three armed clinical trial in R for comparing the Restricted Mean Survival Time

have a three armed clinical trial with two treatments and one placebo. I am to compare the Restricted Mean Survival Time among the three. I need to find the sample sizes for each arms (equal ...
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Using dimensionality reduction to control for more variables in a multiple linear regression without breaking the 15:1 rule - possible?

I'm interested in whether there is a relationship between my particular variable of interest (X) and my dependent variable (Y). I'm planning to explore this using multiple linear regression. My focus ...
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Central Limit Theorem for proportion - np >=10 or 5?

While trying to understand deeper about Central Limit Theorem for proportions, I learned CLT for proportions is based on the fact that binomial distributions can be approximated by normal ...
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Calculation of an appropriate sample size

I am conducting a project in which we are studying a specific biomarker for asthma. This biomarker normally appears in 63% of the population. I would like to know what would be the sample size to ...
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1 answer
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What test to use to see whether the number of patients in the two hospitals is the same?

The number of patients in a given age range attending the Accident and Emergency Services of two hospitals P and Q on independent days are as follows. The days for the two hospitals are independent of ...
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