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Questions tagged [gpower]

G*Power Statistical Power Analyses for Windows and Mac is a program which helps with calculating the power of some statistical tests.

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Do I need to run an “a priori” power analysis before doing a content analysis?

I am planning to do a content analysis of social media posts from different groups, coding categories with categorical (binary) variables (0 = not present, 1 = present). I want to compare group ...
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126 views

Different results for simulated and closed form distribution of T-statistic under the alternative hypothesis

While running some simulations to get a better grasp of the concept of statistical power I stumbled upon an unexpected result. I was trying to simulate the sampling distribution of test statistic $T$ ...
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Power Analysis in G-Power - Mixed Model Anova

I'm an honours student in psychology doing some data analysis at the moment. My research project is coming to a close for data collection, and it seems like we won't reach our initial goal. I decided ...
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Why does G*power calculate the noncentrality parameter in this way?(different from formula)

I'm calculating the power of some F-family tests and I found the key to the power was the noncentrality parameter (ncp). So I'm trying to calculate the ncp $\lambda$. However, I got different results ...
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Repeated measures between factors settings for G*Power power calculation

I want to estimate the sample size by GPower,My experiment design is 2*4*3.I want to know how to setting the "number of measurements" when i use the "F test,ANOVA repeated measures,between factors"?
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Power & Effect Size for Multiple Regression - HELP

2 IV's: Pregnant/Non Pregnant & Physically Active/Not Physically Active 1 DV: Cognitive Functioning (Inhibition - SSRT scores) AIM: Investigate whether there is a difference in physical activity ...
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Which effect size to determine sample size in power analysis for mixed effects model?

Experimental design: 3x12 repeated measures. I ran a mixed effects model that revealed an effect of "variable x" for which there are 12 levels. Post-hoc analyses based on this model (paired samples ...
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1answer
61 views

Power calculations

I am using a toy example to explain power calculations for a t-test Let's say we have two populations where we measure a certain parameter. Population A has a mean of 0 and population B has a mean of ...
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What type of test do I use in G Power?

I've got 1 IV with 2 levels (within-subjects) and 4 VD's (with 7 levels). What type of test do I use in this case ? Thank you
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64 views

Calculating power for balanced incomplete block design

My experiment has a factorial 2x2 design: 2 factors are manipulated at levels 'high' and 'low'. We thus get 4 conditions: Condition 1: Factor A high, Factor B high Condition 2: Factor A high, Factor ...
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59 views

Power analysis for same model as “ANOVA” vs as “multiple regression” yields different results

I have seen posts that said ANOVA and multiple regression are theoretically the same. But if this is really the case, does anyone know why the G*Power (Linear multiple regression vs ANOVA) gives ...
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How to calculte sample size of Mixed ANCOVA(2x2x2) using G*power

I want to know how to calculate the sample size of a Mixed ANCOVA model using the G*Power software. The study design is 2(between)x2(with-in)x2(between) and there ...
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274 views

How is correlation among repeated measures calculated for ANOVA interaction effect?

I am performing a replication study, of an interaction effect found in repeated measures ANOVA. The study is of a 2X2 design (1 group of subjects, 4 measurements each). To estimate the required ...
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1answer
73 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....
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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 ...
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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. ...
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18 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 ...
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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 ...
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101 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 ...
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141 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 ...
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62 views

Determine sample size in power analysis

I have several confusions regarding estimating sample size. Consider the situation where I have data from a pilot, from which I estimated effect size and want to do power analysis (using software such ...
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1answer
37 views

Why is the sample size calculation not in agreement with t-test results?

I used R package pwr (G*Power gives the same result) which say for a one-sided t-test of means with alpha=.05, beta=.20, that I would need 40 samples for both control and treatment groups (n=80) to ...
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81 views

How to get Type II error probability from G*Power

I realize that having standard error of the mean, critical value, sample mean values from a simple a priori power test in the G*Power free download, one could use NORM.DIST in Excel (Argh!) following ...
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262 views

Power analysis for one way anova with post hoc Tukey?

I have an experiment in which I'm doing, among other things, a One way Anova with one dependent variable and 5 groups. After the ANOVA i'm doing Tukey's post hoc to test for differences between groups....
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915 views

Help with G*Power for logistic regression

I need some help understanding what values I need to put into a two-tailed logistic regression power analysis are in G*Power. I am trying to see if hypertension (my binary independent) makes a ...
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73 views

sample size from calculation exceed population size

I calculated sample size from G*Power and got a result of 500. But my population size is just 330. What should I do? For information, I used chi-square test for calculating sample size.
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153 views

How power was calculated in this study

In this high protein study here (http://www.mdpi.com/2072-6643/9/9/1007/htm), comparing high protein to low protein in obese sedentary women, the authors described their methods here An a priori ...
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Why does the estimated sample size decrease as the expected effect gets larger?

Here's a fairly simple conundrum: let's say I'm calculating the sample size needed to determine a correlation of r = 0.7 at 95% power and an alpha (two-tailed) of .05. The null is r = 0 (note I use r ...
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1k views

sample size for difference-in-difference study

I want to do a difference-in-difference study of a prevalence estimate (binary data), but am struggling to find guidance on an appropriate power analysis/sample size calculation procedure. The goal ...
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1answer
49 views

Determining sample size with biased data

I'm new to this forum but I've read a lot of interesting topics to help me in my research, so I'm hopefull someone can help me with this question! My goal: provide management with a sample size. ...
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1answer
383 views

ANCOVA vs multiple regression the same: so why different power analysis results?

This is a general question so I am not supplying details of my experiment. When I search for information on whether to conduct ANCOVA/ANOVA or multiple regression, in many sources including this forum ...
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2answers
414 views

Is it possible for power (1-B) to equal 1?

I'm using a program called GPower to calculate the achieved power of a certain test I've performed. Below is the screen shot of my inputs and outputs. It states that my test achieved a power of 1.0 - ...
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903 views

Chi Square Sample Size Needed with G*Power

I was recommended to try G*Power so I could determine the sample size needed in order to achieve an acceptable power. I'm struggling with picking the test and filling out the appropriate values. ...
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When planning to use Multivariate Regression with some binary categorical predictors, how do I find the sample size I need using G* Power? [closed]

I want to run a multivariate regression data analysis. I have 5 predictors--two of them are binary--and one DV. When planning to use Multivariate Regression with some binary categorical predictors, ...
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2k views

Carry out power analysis for MANCOVA using G*Power

There are helpful questions and answers for how to calculate the required sample size (or carry out a power analysis) for MANOVA, but not for MANCOVA using the freely-available G Power software. Is ...
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205 views

What exactly means corr among repeated measures in G Power? I

Is it test-retest or just correlation between repeated measures?
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1answer
3k views

Power of interactions in factorial ANOVA using G*Power

I’m using GPower to perform a priori power analysis. Let’s say that I want to do a 2x2 factorial ANOVA. I’m interested in the power of the interaction. I set effect size f to .25, alpha value to .05, ...
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507 views

a priori power analysis for ANOVA plus post hoc test

I would like to perform an a priori power analysis to calculate required sample size for data to be analyzed using one way ANOVA and Tukey HSD post hoc test. (I want to determine pair-wise which ...
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1answer
2k views

Unequal Sample Size Effect on Power Calculation

I am new to power analysis and have been experimenting with one-way fixed effects Anova in G*Power (Fixed effects, omnibus, one-way, Post hoc power). When dealing with unbalanced design, the effect ...
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1answer
13k views

How to work out Effect Size for a MANOVA using G*Power

I'm using G*Power to work out how many participants I need. I'll be using a MANOVA, I have two independent variables (Male and Female) and they will be answering 13 different questionnaires so 13 ...