# 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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### Help: G*Power Analysis for Correlation and Moderation

I have 3 measures, all scored on Likert style scales and I will be using the sum of items from each as scores. It is a cross-sectional study. predictor variable is attachment style (with two levels, ...
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### Statistical power of my study

I am writing a paper for a journal. I have been asked to calculate the statistical power of my study. I have zero idea about how to do that. I am an engineer and never cared about this kind of ...
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### Repetitions on the same combination of factors in mixed ANOVA and its power analysis

I am trying to decide the appropriate model and perform power analysis. Suppose a data contains 2 groups (A,B) and 28 participants from each group. All of those participants are measured 15 times on ...
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### Power Analysis for 8x8 factorial within-subjects design (required number of participants/samples)

for an experiment, I was asked to provide a minimum required number of participants using an a-priori power analysis. Thing is, I'm now really confused on how this is possible or even if it makes ...
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### How does G*Power calculate sensitivity in z-test for two independent proportions

I am trying to recreate sensitivity calculation in Python by applying the same methodology as used in G*Power z-tests > Proportions: Difference Between Two Independent Proportions > Sensitivity: ...
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### How to: power analysis with log-normal distributed data

Assuming the following data: ...
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### Is G*Power reliable for logistic regression? It does not seem to account for Hauck-Donner

I've just been introduced to G*Power. The only option I could find for analysing logistic regression is described as: Options: Large sample z-Test, Demidenko (2007) with var corr That seems to ...
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### G*Power sample size calculation for ANOVA

I'm trying to do an a priori power calculation with G*Power 3.1.9.2, but I don't know which test to choose and what to enter in "number of groups" and "number of measurements" for ...
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### Sample size calculation for RM ANOVA; the difference between WebPower package in R and G*Power 3.1.9.7

I've run two sample size calculations with the WebPower package in R and G*Power simultaneously. The conditions I've done are; Case 1 Cohen's f = 0.2756987 Number of groups = 1 Number of repeated ...
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### Would a post hoc power analysis be used for a retrospective chart review and how would this be done?

I'm a novice in research and wondering if I need to calculate power to determine my sample size. My study is about collecting data from all patients that presented to a clinic for a period of 6 months....
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### How to interpret a sensitivity analysis from G*Power for a repeated measures, within factors ANOVA

I am trying to conduct a sensitivity power analysis for a (2x2) ANOVA. The participants all received trials based on color or shape, and items could be either old or new. In G*Power I have the ...
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### Sample Size Question - Population- Multiple Regression?

I am doing a research project for class. Our research questions are as follows: Has news exposure impacted parental decision-making in preparation for the new school year? Has Media exposure to ...
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### Post hoc power analysis options for 2x2 ANOVA and paired t-tests

We recently submitted a manuscript for publication. My advisors never do power analyses, and so the reviewers came back questioning our sample sizes. Lesson learned on my end. One reviewer said "...
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### G*Power repeated measures ANOVA within-within interaction

Suppose that I have 4-by-6 factorial design where both factors are within-subject variables, and I want to perform a repeated-measures ANOVA on the data. Using GPower, I calculate the sample size ...
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### G Power Settings for Friedman Test Comparing Multiple Models

UPdated to convey statistical question: The underlying statistical question is one of which test to use: I have three models against a single dataset. I want to see which model is better. Is repeated ...
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### Power analysis for orthogonal polynomials

Use GPower for power analysis for cubic estimator in orthogonal polynomial regression? I would like to determine the sample size I need in order to find a significant cubic estimator in an orthogonal ...
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### How to estimate sample size needed for a planned comparison between two groups in a between-within ANOVA?

I have a 3X3 repeated measures ANOVA with 3 groups and 3 measurement timepoints. In addition to the omnibus effect, I am interested in comparing the difference in change within two timepoints between ...
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### Power of mixed effects model vs ANOVA repeated measures within-between interaction

I'm trying to estimate the power of a 3X3 longitudinal mixed effects model with 3 groups, 3 measurement timepoints, and participant ID as a random intercept. I know that using the "ANOVA repeated ...
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### G*Power ANOVA repeated measures within-between interaction

I'd love to get a sanity check on a sample size calculation I'm running in G*Power. I'm planning a study with 2 groups and 2 measurement points, aiming for a f of 0.10 because, to my understanding, it'...
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### ANCOVA power analysis using groups differing in sizes

For my research, I'm calculating the required sample with G*Power, using effect sizes estimates. I have 1 scale dependent variable and a 4 x 2 design. I especially care about comparing 1 group to the ...
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### Power Analysis for 2-Way-Anova in R

I did a power analysis to calculate the sample size in GPower. Now I'd like to do the same in R. However, I am not able to figure out how... I found ss.2way but that seems to require different inputs. ...
148 views

### Determine the sample size to validate a bug fix

Using gpower, I would like to calculate the sample size to validate a bug fix. There is a software bug that appears in 3 out of 1000 test runs. I would like to validate a bug fix so that it doesn't ...
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### Statistical power and sample size for Poisson regression: specifying the "mean exposure"?

I am trying to perform an apriori power analysis to estimate sample size for a Poisson regression model. The background is that a RCT is proposed to compare the rate of pill consumption between two ...
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### G*Power - Difference between ANOVA Repeated measures, between factors and ANOVA: Repeated measures, within-between interaction

I have a mixed-ANOVA design: 2 groups (experimental & control) x 4 time points (pre, post, post2, post3), and am using G*Power to calculate the required sample size. My understanding is that the &...
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### Reviewer is requesting the use of Bonferroni adjustment to alpha in G*power calculation ("multiple regression" with 3 predictors)

Since Bonferroni is intended as a (conservative) adjustment to reduce Type 1 error, I'm unclear why it would be required by the reviewer to adjust alpha in the power calculation (using G*power). While ...
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### GPower: unequal number of measurements?

I'm in psych research, so typically I have my subjects do ~40 trials per condition. If I have an uneven number of trials per condition (say, 30 in one and 40 in another) and a 2 x 2 within-subjects ...
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### Multiple linear regression: minimum sample size required when only a subset of independent variables are of interest

I am planning a multiple linear regression model with 1 continuous dependent variable and 6 independent variables. Of these 6 independent variables, I am only interested in the contribution of 2 ...
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### Why are ztest and chisquared test not returning equivalent sample size results?

I'm using the statistical software G*Power to find the minimum sample size needed to detect whether or not the difference in two proportions is statistically significant in an AB test I'm setting up. ...
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### What are the distribution values (mu, sigma) for alternative hypothesis of differences between two proportions? How to calculate?

When comparing two independent proportions (p2, p1) in an A/B test, null hypothesis states that the difference is 0, while the alternative hypothesis states it is something other than 0, let's say mu1....
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### Noncentrality parameter Repeated-Measures ANOVA - formula vs. G*Power

I am trying to figure out the correct expression for the noncentrality parameter $\lambda_{ws}$ for the within-subjects effect in a one-way Repeated-Measures ANOVA with $k$ trials/groups. Comparing ...
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### Formal name for research design: repeated measures, 1 varying treatment condition, 1 constant treatment condition

I'm coming from a background with regards to randomizing treatment and just conducting measurement at one point in time. In my current setup, there are just four groups of interest: A control group (C)...
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### Is there any way to do a power-based sample size calculation if you don't know the minimal (scientifically) important difference?

I am in the life sciences field and I don't have much experience with power-based sample size calculations. I am doing a Western blot experiment and my research question is whether protein X ...
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### Power analysis without a prior and for observational data

I am trying to develop the design for an observational study, but I am struggling with the number of observations that would allow us to estimate our model and generalize its results. As a dependent ...
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### Calculate required sample size for multiple linear regression

I'm planning to run a survey experiment where I have a pre-measurement of my outcome variable, then I'm randomly assigning my respondents to one of six treatments/stimuli ("NO" = baseline ...
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### ANOVA Repeated Measures crossover design, number of measurements in GPower?

I am planning an experiment in which I will have a group of animals which I will give both the control diet also test them on the treatment diet. I think I can use repeated measures ANOVA for this. I'...
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### What does Actual α mean in G*Power?

Can anyone explain what actual α (alpha) means in G*Power? For input parameters, I choose 0.05 for α err prob, and I get 0.0288167 for Actual α. Does it mean I should use 0.0288167 instead of 0.05 for ...
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### GPower: Difference in Sample Size for ANCOVA vs. Repeated Measures ANOVA in clinical trials

I want to conduct a randomized pre-post intervention study with two measurement points (1. Baseline 2. Post-intervention) and two groups (Treatment vs. Control) and am currently trying to work out the ...
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### Regression power analysis: R's pwr::pwr.f2.test R2 deviation from zero vs. R2 increase (vs. G*Power)?

This question is about the difference between R's pwr::pwr.f2.test and G*Power regarding the ...
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### Numerator degrees of freedom in power analysis for regression (R vs. G*Power)

Background In R, the power analysis package pwr can estimate the required sample size for regression with the following formula: ...
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### Power analysis: Use a prio test to determine number of particants with G*Power

I would like to conduct a priori power analysis to determine the number of required participants for my experiment. I want to have two experiment groups (with immersive and desktop virtual reality) ...
1 vote
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### Sample Size - GPower options in F tests, ANOVA: Repeated measures, within factors

I'm trying to determine sample size and found that the "Options" in G*Power 3.1.9.7 changes the effect size (seems to automatically convert this and provides the same results, first two ...
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### Power Calculations for Diff-in-Diff with Fixed Effects

I am conducting a field experiment. Where we observe two different optimization methods. First 7 days pre-treatment period and 28 days treatment period. To split treatment and control, we will have ...
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### Odd sample size in GPower (Repeated Measures ANOVA, within factor)

I am going to conduct a pretty simple experiment: one within factor with 8 levels for a single group of participants. I'm trying to determine the apporpriate sample size using GPower based on an ...
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### ANCOVA controlling baseline in RCT - power analysis and sample size questions

I am performing a power analysis/sample size estimation for an RCT. We will be controlling for baseline symptoms and using post-treatment or change scores as our outcome variable. This design is ...
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### Calculating sample size with power analysis

I have to calculate the sample size for an experimental study and took some sample distributions data from a previous similar research and calculated the means and standard variations for before and ...
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### G*Power settings to find minimum sample size for a 2x2x3 design

For a power analysis, does "number of measurements" refer to the number of LEVELS or the total number of CONDITIONS? I have a three-way (2x3x2) ANOVA that is entirely within-subjects, and I'...
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### G*power -> MANOVA (global effects) confusion with given effect size

I'm working with G*power to calculate the sample size for my experiment. At the moment I'm a little bit confused handling the effect size values. I have 3 IV (3 groups) and 2 DV => so i will use ...
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### Calculate sample size for linear regression [duplicate]

I have a total of 9 independent variables (IVs) and 1 dependent variable (DV). 2 of the IVs are binary and the other IVs are continuous ranging from 0 to 5. The DV is continuous ranging from 0 to 5000....
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### Would a repeated measures MANOVA be appropriate for a 9DV, 2IV within subjects study design?

I am trying to get an estimate of participants to strive for in my study. Being rather new to the research and stats scene, I was hoping the community could help me out a little bit? The study has 9 ...
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