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: ...
ThePresident's user avatar
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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 ...
Thea's user avatar
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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 ...
Benji's user avatar
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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'...
Benji's user avatar
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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. ...
Julian R.'s user avatar
5 votes
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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 ...
user167591's user avatar
3 votes
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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 ...
J Gates's user avatar
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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 ...
The_old_man's user avatar
2 votes
2 answers
134 views

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. ...
Pedro Alonso's user avatar
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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....
kukushkin's user avatar
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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 ...
Barlon Mrando's user avatar
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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)...
rpickmans's user avatar
3 votes
1 answer
315 views

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 ...
David Harar's user avatar
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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'...
Shara's user avatar
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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 ...
Fatemeh's user avatar
3 votes
1 answer
3k views

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 ...
rempsyc's user avatar
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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: ...
rempsyc's user avatar
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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) ...
datasciencelearner's user avatar
1 vote
1 answer
1k views

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 ...
adrienne's user avatar
1 vote
0 answers
160 views

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 ...
flw's user avatar
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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 ...
SimpleSaze's user avatar
4 votes
2 answers
867 views

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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2 answers
482 views

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 ...
randomname's user avatar
1 vote
0 answers
234 views

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'...
Chloe L.'s user avatar
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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 ...
Tom's user avatar
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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....
Jensxy's user avatar
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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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How to interpret sensitivity power analyses?

Journals and reviewers increasingly ask authors to systematically report sensitivity power analyses. I know that a sensitivity power analysis allows you to determine the minimum effect size that the ...
rempsyc's user avatar
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