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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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5 views

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 ...
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 $T$ ...
38 views

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 ...
21 views

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 ...
11 views

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"?
30 views

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 ...
24 views

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 ...
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 ...
16 views

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
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 ...
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 ...
59 views

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 ...
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 ...
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....
63 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 ...
87 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. ...
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 ...
21 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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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....
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 ...
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.
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 ...
28 views

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 ...
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 ...
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. ...
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 ...
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 - ...
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. ...
46 views

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, ...
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 ...
205 views

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

Is it test-retest or just correlation between repeated measures?
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, ...
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 ...