All Questions
Tagged with gpower statistical-power
63 questions
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Bootstrapping as an alternative to simulation-based power/sample size calculations
Typically when one has to do a sample size and/or calculation, they might use simple sample size calculations from textbooks or use gpower. However, there are only closed form calculations for very ...
- 629
2
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41
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How can I convert an effect size from Cohen's d to f(v)
I am interested in calculating the power I need to compare several groups to one reference group in how much an outcome changes between two timepoints. My understanding is that I should use the ANOVA: ...
- 413
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29
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Sample size estimation using G*Power
I am trying to calculate an a priori sample size using the G*Power for a project that I intend to do. I will collect reaction time data from two groups of participants across two time points (T1, T2). ...
- 43
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41
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Mixed ANOVA Power Analysis
So I'm doing a thesis on compassion meditation and I'm confused about the power analysis. When I calculated it in G*power, "total sample size= 34", but it's for a 2x2 mixed ANOVA, so does ...
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12
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Predictor variables vs control variables for power analyses in multiple regression G*Power
I am using GPower to get an idea of the sample size needed to detect a medium effect size in the second and third steps of a hierarchical multiple regression model. To do this, GPower asks for the ...
- 315
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21
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G*Power sample size calculation between regression coefficients in two separate within-subject models
I have two identical regression models run on two different subsamples. In R, my models would be the following:
...
- 65
1
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1
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66
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Power of One Sided t-test
Let $X_1, \ldots, X_n$ be a sample from $N(\mu, \sigma^2)$ for unknown $\mu \in \mathbb{R}$ and unknown $\sigma > 0$. Fix $\mu_0 \in \mathbb{R}$. The one-sided hypothesis is $H_0: \mu \leqslant \...
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27
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G*Power Mixed two-way ANOVA power analysis - sample size seems too small? [duplicate]
I am running my first-ever power analysis and I am worried that I am misunderstanding something about G*Power. I am running a 2x2 mixed ANOVA. I chose the 'ANOVA: Repeated measures, within-between ...
- 43
3
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1
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133
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Approximate power analysis for simple linear mixed model without random effects
For educational purposes, a repeated measure of all participants in two conditions is modeled as linear mixed model. We're interested in the difference in outcome while controlling for confounders $...
- 247
5
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1
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627
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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 ...
- 185
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46
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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 ...
- 119
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77
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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 ...
4
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104
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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: ...
- 213
1
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1
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539
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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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604
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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 ...
- 153
3
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1
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169
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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 "...
- 153
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697
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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 ...
2
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1
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731
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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'...
- 413
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436
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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.
...
- 11
5
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1
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180
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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 ...
- 151
3
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1
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2k
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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 ...
- 923
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1
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2k
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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 &...
- 31
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1
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59
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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 ...
- 23
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2
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151
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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. ...
- 271
1
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30
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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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3
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1
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356
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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 ...
- 233
1
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1
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57
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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 ...
- 334
3
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0
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86
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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 ...
- 581
3
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1
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4k
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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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4k
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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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1
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4k
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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:
...
- 291
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24
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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
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0
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170
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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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5
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3
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1k
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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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2
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573
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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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282
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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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1
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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 ...
- 291
1
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0
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234
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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 $T$ ...
1
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1
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308
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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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1
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0
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63
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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 ...
- 11
3
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1
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481
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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 ...
- 4,591
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0
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276
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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 ...
3
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1
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2k
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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 ...
- 99
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1
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674
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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....
- 604
4
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0
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73
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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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1k
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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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1
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0
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800
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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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3
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1
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193
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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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1k
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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....
0
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0
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1k
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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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