# power-analysis's questions - English 1answer

520 power-analysis questions.

### Determining sample size for minimum detectable effect in a finite population?

0 answers, 14 views sampling power-analysis
I am running a longitudinal experiment on 75 plants. For logistical reasons, there is no control group -- all plants receive the treatment. To assess the outcome of the experiment, I need to run a ...

### 3 Should you be concerned with statistical power if you reject the null hypothesis?

1 answers, 35 views power-analysis power frequentist
My understanding of statistical power is that it is the likelihood of correctly rejecting the null hypothesis, with low power meaning you are very likely to make a beta error (failing to reject the ...

### How to conduct a Power Analysis for a Factorial Design in R?

0 answers, 8 views r power-analysis power
I have installed the R package "pwr" and I am looking to use it for my experiment to see how much power the tests will have. The experiment is a $3^3$ factorial design ($3$ factors, each with $3$ ...

### 1 How can I be sure my sample size is large enough for conditional logistic regression?

1 answers, 361 views r logistic power-analysis
I am performing a conditional logistics regression (CLR) case-control (1:3) study over a very large dataset that has been partitioned according to a set of study requirements (to follow). Each entry ...

### 2 Finding the power function of the given test

0 answers, 36 views hypothesis-testing power-analysis
We have a density $X$ defined as $f(x,\theta)=\theta x^{\theta -1}I_{(0,1)}(x)$. The hypothesis to test is given as follows: $H_0:\theta \leq1$ Vs $H_1:\theta >1$ A sample size of two is selected,...

### Simulating post hoc power for multiple regression

I have a null result for a negative binomial regression model and I would like to give evidence that my sample is large enough to detect even small effects. I've found a few online calculators for ...

### Sample size calculations for comparing area under curve (AUC) in ROC analysis in R

0 answers, 26 views r sample-size roc power-analysis auc
I have a dataset with a response variable and a predictor variable. I want to calculate the possible difference of AUC (delta) I can find with power = 0.8 and significance level = 0.05. Let's say I ...

### 1 How would someone name a “kind of” post hoc power analysis using a priori mean difference estimates?

0 answers, 9 views t-test power-analysis power post-hoc
Imagine a researcher conducted an experiment and tested an hypothesis using a two independent samples approach. It was the first experiment of this kind, so the researcher had no idea about a possible ...

### Cohort Study Sample Size and Multiple Comparisons

I'm designing an epidemiological retrospective cohort study with a large number of exposures and outcomes, and I'm trying to figure out how many subjects I'll need in order to run all my analyses. The ...

### 6 How to do a power analysis for an unbalanced mixed effects ANOVA?

I need suggestions for how to calculate the $n$ required for 80% and 90% power for >30% change from baseline ($T_0$) at $T_1$ or $T_2$, drug vs. placebo, 2:1 ratio; 20% CV in test; factors: subject, ...

### How to Calculate Sample Size for a two samples Welch's t test given a wanted power for an expeted effect size (without R)?

I have found no answer on web search engines for that. And even though I was able to find here some answers on how to calculate the power of a Welch's t-test here, they were expressed in R code. As I ...

### “effect size is independent of sample size” really?

1 answers, 38 views sample-size effect-size power-analysis
I keep reading "effect size is independent of sample size" on the interwebs. Don't get me wrong, I get the practical vs statistical significance considerations. What I don't get is that; -power,...

### Power calculation for ordered logit regression in R or Stata

0 answers, 21 views r stata power-analysis ordered-logit
I am trying to estimate the sample size needed to have an effect size of 2.4, with power=0.8 and alpha=0.05. The outcome variable has 8 levels and each individual has 8 observations. The model has ...

### Testing nested random effects in power analysis

I would like to estimate the power of an average treatment effect, across a cohort split into subjects nested in sites. I provide a complete code example below that generates fake data given hyper-...

### 1 Sample size for multiple regression using G*Power

I am running a study on school children to compare psychometrics in physically active and sedentary children. My IV is physical activity with 2 levels - physically active / sedentary and DV ...

### 2 Power calculation for Spearman correlation

1 answers, 48 views r power-analysis spearman-rho
Suppose, I am generating data from bivariate normal distribution with means 0 and variances 1 and correlation coefficient 0,0.5 and 1. I need to calculate power for different correlations. I am doing ...

### How can you compute sample size for a linear mixed model? G*Power only does repeated measures ANOVA

1 answers, 40 views mixed-model sample-size power-analysis
I read everywhere that repeated measures ANOVA is inferior to mixed modelling (since it doesn't handle missing data as well and relies on sphericity assumption). G*Power doesn't tell you how to ...

### 1 Carry out power analysis for MANCOVA using G*Power

1 answers, 993 views power-analysis manova gpower
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 ...

### Optimal Sample Size/Power Analysis for Panel Data

I'm running a economic experiment. From a previous pilot I already know which size of treatment-effect I can expect. Each participant plays 20 rounds, so it't a repeated measures approach. I want to ...

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

1 answers, 10.416 views anova effect-size power-analysis manova gpower
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 ...

### Puzzling sample size on a within-between interaction

0 answers, 17 views power-analysis power gpower
I have a question about an a priori statistical power analysis. I am used to using between-subjects experimental designs, in which I usually need about 180 participants, using a small to medium size ...

### 3 Sample size to detect decrease in standard deviation

1 answers, 45 views hypothesis-testing power-analysis
Running into a little bit of an issue with an experiment. Basically, I'd like to make a change in a process that may or may not reduce the variation in production. The mean value of the process is ...

### G*Power 3.1: Computing Numerator df for factorial ANOVA for a priori sample size computation

0 answers, 12 views anova power-analysis gpower
I have looked everywhere and have not found an answer to my specific design question related to computing the sample size necessary for (specifically) a 2 X 2 X 2 ANOVA. Specifically, using G*Power ...

### 2 Determining power of statistical test through bootstrapping

2 answers, 60 views bootstrap power-analysis power
I'm trying to understand what's happening in the article Using simulation to estimate the power of a statistical test I'm familiar with bootstrapping which makes sense to me. But I don't understand ...

### 1 Power Calculation in R for CRCT with outcome on individual level

I would welcome any help with computing power calculations for cluster randomised control trial and specifying the code in R for this. I've been trying to use clusterPower package but any R package ...

### 1 Do you need to calculate sample size to evaluate a new diagnostic test?

I am writing a grant application which will be evaluating a new diagnostic test. The test will predict whether a patient with lung fibrosis will remain stable or progress. I am using an existing ...

### Calculating trial size with the pwr package (R)

1 answers, 23 views power-analysis clinical-trials
I'm attempting to calculate n for a trial in medical imaging comparing two different imaging modalities. I've never done this before, so I'm not sure how to approach this and interpret the result. ...

### 1 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 ...

### 1 Detecting significant effects based on critical t value for a given sample size

"Because (this study) collected 77 participants in total, and used an alpha level of .05, the critical t-value is 1.99. This critical t-value can be transformed into a 'critical standardized effect ...

### 3 Which statistical test is appropriate if we can not measure normality

Say I have two devices that purifies milk, device A and device B. I assume Device B is better and it produces milk that is 5% better than A. If I want to test this assumption, I take 8 sample from the ...

### How to calculate sample size for study design where observations are nested in study site?

I need to estimate the required sample size for a future study with a nested design and thus, mixed effect regression. Sampling will take place at six plots per study site and observations will thus,...

### 1 Are my statistically significant results invalid if I fail to reach my desired sample size?

0 answers, 13 views sample-size power-analysis power
I conducted an unfunded study where 3 groups of 15 participants were observed over 11 timepoints. There were statistically significant between-group differences in slope and also statistically ...

### 1 Power analysis for circular data

1 answers, 13 views power-analysis circular-statistics
Imagine I have a sample distribution for a circular data set with a mean group direction and known variation. I would like to do a power analysis for a known effect size (e.g. to determine what sample ...

### 2 Does the effect size mean the expected difference between the means

I am designing an experiment and want to define the sample size. To identify this, I am setting my significance level to 0.05 and the power to 0.8. My alternative hypotheses says the two means should ...

### 3 Interpretation of power and detectable difference

I know power is the likelihood of correctly rejecting the null hypothesis, but I just want to check that my interpretation of it with the detectable difference is correct. Consider a 2 sample test ...

### Gpower: Correlational power analysis

1 answers, 11 views correlation power-analysis
I would like to perform a power analysis on Gpower. The only bit of information that I have is provided in the image below: This is what I have done so far: Am I doing it right ? Thank you

### power calculation with SD as outcome

0 answers, 19 views standard-deviation power-analysis
I have a study where I need to estimate the needed sample size to reliably determine the SD. In this case the means are irrelevant, as only the SD carry meaning. I have tried to find a solution for ...

### -1 Consequences of conducting under-powered trials?

I have been taught that under-powered trials cause effects of practical importance being not detected. Thus, that's the reason why we mainly work with power >= 0.8. However, I'm curious.. In what ...

### 1 Weak Sample Size & Low Statistical Power

I have a problem of sample size for my research paper approval. I could only ran the statistics on 5 subjects for both plantar pressure and temperature measurements but the statistical power seems to ...

### What do the authors mean with “within-between factors” in this power calculation?

0 answers, 11 views anova power-analysis gpower
I have a chunk of text and I cannot work out what the authors are trying to say with within-between factors. Why does the power requirement go from 58 to 18? Statistical power analysis was ...

### power analysis with different sample distributions

0 answers, 14 views power-analysis skewness
I need to perform a (two-sample) power analysis, however my data are differently distributed in both samples and I am not sure whether I can a standard approach through t-test. Please see the ...

### 2 Power of chisquared test for large sample size

I would like to calculate the power of a Chi-Square test for goodness-of-fit as a function of sample size for a specified alpha-value (say 0.01). Specifically, I am referring to power as the ...

### What kind of test has multiple within-subjects factors ONLY and what variables do you need to simulate the test for a power analysis

I need to run a power analysis in order to discover a sample size for an experiment. The majority of experiments our lab runs are repeated measures studies that use no between subjects variables but ...

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

1 answers, 24 views sample-size power-analysis gpower
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 ...

### 3 Adjusting any power analysis with FPC?

Is it correct (perhaps at least as a good approximation) to determine sample size via a power analysis that assumes an infinite population and then to adjust the required sample size by a finite ...

### 4 Can I trust the result of a one-way ANOVA with many treatments each with very few replicates

I am doing a one-way ANOVA of a response variable (Y) on a treatment factor (T) of 7 levels. However, for each treatment, I have only 2 observations (or replicates). The ANOVA result shows the the ...

### How do I calculate sample size of this study using G-Power

0 answers, 36 views regression anova power-analysis
I am investigating the effects of learning on cultural distinctive school children’s academic performance from a root cause of Social Mediation which has three categories: cultural language, ...

### 1 At what sample size does the precision of estimate stabilise?

Imagine I have a population of a known size (e.g., 100,000 voters), and I know they can only vote for A, B, C, D or E. If a random sample of 100 voters are, e.g., A = 40%, B = 30%, C = 10%, D = 10%, ...

### How can I estimate the power of a MaxDiff experiment with covariates?

I am running a MaxDiff experiment where there will be four different "arms". Essentially, a respondent will be assigned to one of four conditions, where they will be shown one of three messages (plus ...

### Sufficient sampling size for logistical regression observational data

0 answers, 16 views logistic power-analysis cluster-sample
As a part of my master thesis, I'm conducting an observational study of journalists' background and the effect of this on the approach to a certain case study. I have a fixed number of observations/...