# Questions tagged [power-analysis]

An inquiry into the quality of a statistical test by calculating the power - the probability of rejecting the null hypothesis given that it is false - under certain circumstances. Power analysis is often used when planning a study to determine the sample size required to achieve a nominal level of power (e.g. $80\%$) for a given effect size. In many situation theoretical calculations are intractable so power analysis is done by simulation.

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### non central chi square distribution and the non centrality parameter in R [closed]

I want to examinate the power of two sample t test in detecting a shift delta = 2 so i must generate two samples x<-rchisq(10,3) and ...
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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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### What to do if the data collection company accidentally gathered more data than we need?

This is actually a true story. While planing a study, my work colleague did a power analysis for an intended effect size and a priori power of 80%. It turned out that the required sample size was one ...
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### How to calculate power of sample size a posteriori for GLMM

I conducted a study with 3 different groups of participants (n = 25, n = 27, and n = 26) and three phases (baseline, treatment, post-test). I analyzed my data using a mixed-effects binomial logistic ...
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### How do I run a power analysis for a 2x2x2 ANOVA?

I have a 2(between) x 2(within) x 2(within) design and would like to calculate the a-priori power needed to detect a three-way interaction using an ANOVA. I've read that this can't be done using power ...
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### Should I remove a significant covariate from my mixed-effects model because it's underpowered?

I tried figuring out the answer by reading the comments in this thread but I am still confused. Should I remove a covariate from analysis when it comes as significant but power simulations finds that ...
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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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### Sample Size Calculation - Two Independent Means

I am trying to design an email test to measure the demand lift obtained from a marketing promotion (treatment) versus no promotion (control). To do so, I want to calculate the per-group sample size ...
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### Nested Experimental Design: Intuition about power?

I am planning a nested experimental design, where 1000 participants respond to one policy proposal coming from a 2^3 design (125 participants for each condition A x B x C). Yet, the policy proposal ...
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### Power analysis for Ordinal Regression

I am looking for a resource to conduct power analysis for an ordinal regression that includes several predictors (there is no "treatment group"). I found a great simulation method first ...
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### How many repetitions to establish difference

(Real-world Context: I often make changes to code, which I suspect will have small impacts on the performance. i.e. improvements that lie within the natural variation of the code's runtime. How many ...
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### Power of combined hypotheses test of two separate hypotheses

In a manuscript that I've read, the primary objective is to detect the effect of a treatment. To be able to generalize the statement, two different species (mice and rats) are included in the study. ...
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### Sample size to test a three-way interaction

I'm want to run a study with 2 categorical IVs and 1 continuous IV. The DV is continuous. It's my understanding I will need to run a multiple regression to test the effects. How do I determine the ...
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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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### Wilcoxon-Rank-Test / Variance heterogeneity and skewed normal distribution / Power Simulation

I observe results that I cannot explain directly. I have created a simulation study where the data generating process follows a skewed normal distribution where the parameters of mean and variance are ...
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### Sample size cutoff for agreement coefficients

New poster here. Would love some help thinking through this. Suppose I am observing individuals in public space, and I am recording the number of occurrences of a target behavior (e.g., looking at a ...
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### minimal detectable effect size in linear mixed model

I'm trying to find the minimum detectable effect size (MDES) given my sample, alpha (.05), and desired power (90%) in a linear mixed model setting. I'm using the ...
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### Analytical power analysis of a binomial RCT

I have a certain population of users of my free app, with new ones installing every day. I want to run an RCT on them, specifically measuring the impact of some change on their conversion rate (i.e. ...
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### Simr: Post hoc power 0% and non signfiicant but effect size 0.3

I set up a glmer model via the package lme4. Using a likelihood ratio tests I compared several models. Two main effects were ...
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### How to use Power Spectral Density in a Linear Regression

I’ve computed a vector-valued autocorrelation function $\phi_{xy}(t)$. Because I use an exponential kernel, $\phi$ is pre-windowed. In the discrete world, phi is a 3D matrix (num inputs by num outputs ...
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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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### power analysis for correlations

Does anyone know of a good method to run a power analysis for correlations whilst taking into consideration the number of trials of the task? I have used the package pwr in R to look at power but it ...
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### How do I report the power calculation when I am performing calculations on the whole population?

I am putting together a bid which states: "you should provide information about both your issued and achieved sample sizes, along with appropriate power calculations". The dataset I am using ...
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### Calculate power for a cumulative link model, a categorial logistic regresssion in this case with G*Power

I want to calculate the power of a logit model. In R I used the clm function. I know, it is only possible to calculate an approximation. I want to use G*Power for the calculation. But I'm asked to ...
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### Estimating sample size in a penalized bernoulli regression

In response to this post Frank Harrell suggests a minimum sample size per sub-group of $n=96$ for penalised Bernoulli regression. I was wondering where he might have got that number from. A paper? or ...
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### Analysis plan and Power analysis for nonparametric test with repeated measures

I am conducting a study where each participant goes through 8 trials with a binary outcome variable (i.e., Yes/No). There are two groups, call them A and B. Based on how I am setting up the study, my ...