Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

0
votes
0answers
12 views

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 ...
0
votes
1answer
16 views

G*Power and simulation produce very different sample size estimates for a Poisson regression

I've been attempting to conduct a sample size calculation for a Poisson regression. G*Power produced a sample size of 472. Parameters for G*Power Tails = 2 Exp(B1) = 1.233 alpha = 0.05 Power = 0....
2
votes
2answers
61 views

How to calculate the effect size for a t-test?

The pwr package includes the function pwr.t.test, which relates the following four quantities: sample size effect size ...
0
votes
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 ...
0
votes
0answers
10 views

Should I test for sphericity and calculate statistical power before running and modelling any forecasting model?

I'm trying to model a regression for one dependent and five independent macroeconomic variables. I'm new to statistics but I've read lots of text books and articles about SEM, cointegration, ols, URT, ...
2
votes
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 ...
4
votes
0answers
54 views

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 ...
0
votes
0answers
3 views

Clustered or blocked? Running power analysis for DIM

I am working with the following design: -80 districts, each district paired using matching and half assigned to T1 and the other to C1 -All sub-districts within a district (let's say 10) receive T--> ...
0
votes
0answers
9 views

power analysis for interaction of three within-subject factors

I am trying to find an example of power analysis for an interaction effect of three within-subject factors (each factor has 2 levels). I found only an example for an r code simulation with 2 factors, ...
3
votes
2answers
50 views

Power analysis for logistic regression with dummy independent variables

Per reviewer request, I need to do power analysis for a logistic regression model with multiple dummy variables. I have four groups: Control, (Treatment) A, B, and C. The hypothesis is that group A ...
2
votes
1answer
21 views

Sample size calculation for Kendall's Tau in reproducibility study

Can anyone help with justifying (or rubbishing) a couple of aspects of a sample size calculation for a grant proposal. A pilot study gave significant results for the correlation of a continuous (non-...
0
votes
0answers
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 ...
0
votes
0answers
28 views

Can I break up observational window in order to increase sample size?

I want to compare a tasks completed in the morning to tasks completed in the evening. The participants are given 4 hours to complete the tasks. I will do a t-test to compare the effectiveness of the ...
0
votes
0answers
7 views

Measurement theory and sample size calculation for multivariate testing

Let $\mathbf{Y}$ be a vector of independent, normally-distributed random variables. Let $S_1$, $S_2$ and $S_3$ be three non-overlapping samples of sizes $N_1$, $N_2$ and $N_3$, respectively. Let $M_A$ ...
1
vote
0answers
14 views

Power analysis for contingency table

Following a cardiac surgery a patient will be classified into one of four categories: Nothing, Mild, Moderate, Severe. There is a new test which, when performed after the surgery, claims to be able to ...
0
votes
1answer
24 views

How to compensate for different statistical power in multiple comparisons? [closed]

Imagine we are performing 10 comparisons on a single variable of choice. The 10 respective experiments have different statistical powers. Now imagine that the least powerful and the most powerful ...
0
votes
0answers
20 views

Sample size calculation: difference between 'linear multiple regression test' & 'linear bivariate regression' test G*Power 3.1

I am trying to calculate a sample size using G*Power 3.1 for a linear model with multiple independent variables, but only two "primary" predictors of interest plus an interaction term between them. ...
0
votes
0answers
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 ...
1
vote
0answers
22 views

Question about necessary experimental recruitment size given particular design

Suppose each individual faces a series of test-rounds, each a part of a broader task. In each round, they face some probability that the task ends, and some probability they continue to the next round....
1
vote
0answers
30 views
0
votes
0answers
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%, ...
0
votes
0answers
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 ...
0
votes
0answers
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 ...
0
votes
0answers
16 views

GPower Sample Size Error with Large ANCOVA Model

I am trying to do a power calculation that with a very large ANCOVA model but am getting an error because my number of groups is too large. I have 14 binary variables, two 4 factor variables, a 5 ...
0
votes
0answers
22 views

Ordinal logistic GEE sample size estimation

I am looking for ways of doing power analysis for ordinal logistic GEE (currently in SPSS, but open to attempting R or something else). My understanding is that this will not be possible in software ...
2
votes
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 ...
0
votes
0answers
15 views

Power analysis nested design

I have some pilot data and I want to use it to do a power analysis and find out how many replicates I need. The design is: 4 locations (IV, ID, KV, KD) -> 3 containers per location (L, M, R) -> 4 sets ...
0
votes
1answer
26 views

Unbalanced Longitudinal Multilevel Model Power Analysis

I am trying to conduct a power analysis on a multilevel longitudinal model (pre-existing household panel dataset) and am having trouble figuring out how to do it (or if it is even needed in the first ...
0
votes
0answers
11 views

Power analysis for non-inferiority study

I'm doing a power analysis for a non-inferiority study based on this calculation from "Sample size calculations in clinical research" by Chow, Shao, Wang, and Lokhnygina: $$ n = \frac{(z_{\alpha}+z_{\...
0
votes
0answers
13 views

What is the correct number of measurements and groups in the following Design?

I using GPOWER: "Anova repeated measures within factors" and need help in giving a correct number to the following inputs: Number of groups. Number of measurements. The design is as follows: I have ...
3
votes
1answer
41 views

Should you be concerned with statistical power if you reject the null hypothesis?

My understanding of statistical power is that it is the likelihood of correctly rejecting the null hypothesis, with low power meaning you are very likely to make a beta error (failing to reject the ...
0
votes
0answers
19 views

How to conduct a Power Analysis for a Factorial Design in R?

I have installed the R package "pwr" and I am looking to use it for my experiment to see how much power the tests will have. The experiment is a $3^3$ factorial design ($3$ factors, each with $3$ ...
0
votes
1answer
18 views

Simulating post hoc power for multiple regression

I have a null result for a negative binomial regression model and I would like to give evidence that my sample is large enough to detect even small effects. I've found a few online calculators for ...
1
vote
0answers
11 views

How would someone name a “kind of” post hoc power analysis using a priori mean difference estimates?

Imagine a researcher conducted an experiment and tested an hypothesis using a two independent samples approach. It was the first experiment of this kind, so the researcher had no idea about a possible ...
0
votes
0answers
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 ...
0
votes
0answers
19 views

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 ...
0
votes
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,...
0
votes
0answers
29 views

Power calculation for ordered logit regression in R or Stata

I am trying to estimate the sample size needed to have an effect size of 2.4, with power=0.8 and alpha=0.05. The outcome variable has 8 levels and each individual has 8 observations. The model has ...
0
votes
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 ...
2
votes
1answer
113 views

Power calculation for Spearman correlation

Suppose, I am generating data from bivariate normal distribution with means 0 and variances 1 and correlation coefficient 0,0.5 and 1. I need to calculate power for different correlations. I am doing ...
0
votes
1answer
38 views

Optimal Sample Size/Power Analysis for Panel Data

I'm running a economic experiment. From a previous pilot I already know which size of treatment-effect I can expect. Each participant plays 20 rounds, so it't a repeated measures approach. I want to ...
0
votes
0answers
27 views

Puzzling sample size on a within-between interaction

I have a question about an a priori statistical power analysis. I am used to using between-subjects experimental designs, in which I usually need about 180 participants, using a small to medium size ...
3
votes
1answer
49 views

Sample size to detect decrease in standard deviation

Running into a little bit of an issue with an experiment. Basically, I'd like to make a change in a process that may or may not reduce the variation in production. The mean value of the process is ...
0
votes
0answers
27 views

G*Power 3.1: Computing Numerator df for factorial ANOVA for a priori sample size computation

I have looked everywhere and have not found an answer to my specific design question related to computing the sample size necessary for (specifically) a 2 X 2 X 2 ANOVA. Specifically, using G*Power ...
1
vote
0answers
20 views

Power Calculation in R for CRCT with outcome on individual level

I would welcome any help with computing power calculations for cluster randomised control trial and specifying the code in R for this. I've been trying to use clusterPower package but any R package ...
2
votes
2answers
91 views

Determining power of statistical test through bootstrapping

I'm trying to understand what's happening in the article Using simulation to estimate the power of a statistical test I'm familiar with bootstrapping which makes sense to me. But I don't understand ...
1
vote
2answers
102 views

Do you need to calculate sample size to evaluate a new diagnostic test?

I am writing a grant application which will be evaluating a new diagnostic test. The test will predict whether a patient with lung fibrosis will remain stable or progress. I am using an existing ...
0
votes
1answer
29 views

Calculating trial size with the pwr package (R)

I'm attempting to calculate n for a trial in medical imaging comparing two different imaging modalities. I've never done this before, so I'm not sure how to approach this and interpret the result. ...
1
vote
0answers
42 views

4x2 within-subjects ANOVA power analysis to detect sample size

I am planning a research experiment with a 4x2 within-subjects design, and am currently trying to determine an appropriate sample size for my project (in order to achieve desired power with an effect ...
3
votes
1answer
33 views

Which statistical test is appropriate if we can not measure normality

Say I have two devices that purifies milk, device A and device B. I assume Device B is better and it produces milk that is 5% better than A. If I want to test this assumption, I take 8 sample from the ...