An inquiry into the quality of a statistical test by calculating the power - the probability of rejecting the null hypothesis given that it is false - under certain circumstances. Power analysis is often used when planning a study to determine the sample size required to achieve a nominal level of ...

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25 views

Simulation of logistic regression power analysis - output given

This question is in response to an answer given by @gung in regards to this question I am also wanting to use simulation to conduct a power analysis on a multiple logistic regression. To keep it ...
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25 views

Multiple Logistic Regression power analysis

So I have a logistic regression model and output an R² value. I then go and add another predictor variable to a second model. I can output a new R² value associated with the second model. When I run ...
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27 views

Sample size for logistic regression with a random effect

I wish to dig out a sample size (or to do a power analysis for a given sample size) for a logistic regression model with a random effect. To simplify, let's say I have a binary dependent variable Y ...
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13 views

How should a sensitivity power analysis be interpreted?

I recently ran an exploratory experiment which manipulated several factors in a full factorial design. There were some clear visual patterns in the results, and a basic ANOVA found several different ...
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15 views

Post hoc power analysis in genetic study

We have performed a genetic study and a post-hoc power analysis is requested. Subjects have been divided in group A (n=162) and group B (421) on the basis of their expressed phenotype. The subjects ...
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0answers
31 views

Power calculations for proportions, two-stage cluster

I am trying to do power calcs for a survey. It's not an RCT, so I have encountered a dearth of material on this. We are trying to estimate a proportion within a population, and have two stages of ...
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34 views

Sample Size for Comparing two Measuring Tools

Let's say I have two devices that measure the same thing: the thickness of an object. Knowing that device 2 is more accurate and precise, I wish to see how accurate device 1 (how close do the readings ...
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2answers
121 views

Adjustable sample size in clinical trial

Most clinical trials I see have a fixed sample size. In some cases they have prior data that allows estimating the effect size and the variance or distribution of values, and calculate the sample ...
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0answers
34 views

Why am I finding greater power with a coarser level of randomization?

I am working on a Monte Carlo power analysis for an experiment about the hiring of teachers in schools. We can randomize the treatment at the school level or at the applicant-school level. I was ...
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12 views

x and y standard deviation estimates in linear regression power analysis

I want to run a power analysis on linear regression against the null that the slope is equal to zero. Specifically I am trying to estimate what sample size I will need to obtain a specific power level ...
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1answer
79 views

Post-hoc power size calculation

I have, probably, a simple problem. I've finished analysing the results of an observational prospective study conducted in our unit. In this study I evaluated if a specific biomarker is independently ...
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2answers
26 views

How to choose the sample size for a pilot study for making a power analysis?

Suppose one would like to test some new hypothesis, for which there are no previous data available. To estimate the needed sample size, one should do a power analysis. Since there are no previous data ...
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35 views

Power analysis for regression with multiple mediators using bootstrapping (PROCESS)

I am currently trying to help a friend of mine with some statistical analyses for her master project, and she has come up with this question, which might be of interest to others (wel'll see) and to ...
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31 views

How to determine how much of the variation in a binary dependent variable can be determined from a set of independent variables?

I'm working with a dataset of legislative voting results in the brazilian Chamber of Deputies. I have a list of votes (mapped as 1 and 0 for Yes and No), like: ...
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49 views

How to calculate statistical power of Wilcoxon signed-rank test in R?

I have two paired samples following normal distributions N(0, $\sigma_1^2$) and N(0, $\sigma_2^2$). Samples represent estimation errors (residuals) of two linear regression models used to predict the ...
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0answers
11 views

Is there software to do a sample sizing for a study based on rate ratio that takes into account matching?

I am searching for software that does sample sizing based on rate ratios that takes into account for matching. Google searches reveal two papers on the first two results ...
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24 views

Confirming failure to reject null hypothesis in Fisher's exact test

I have the following data and am trying to determine if the manual treatment is better at getting a correct response in each category (confidentiality, authenticity, and integrity): Using Fisher's ...
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2answers
59 views

Using Kruskal Wallis vs One Way Anova with small sample size

I have an experiment with one factor and five levels. The response is proportion of conversion (ex: 1/11, 1/8...). Doing a power analysis: ...
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1answer
54 views

A question on accuracy of hypothesis testing

If I am doing a hypothesis test with a sample of 100 from a population of 1,000 it would be more precise than doing a test with a sample of 100 from a population of 100,000. How can I show this? Is ...
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40 views

Power Analysis for Logistic Regression with one nominal variable

How do I estimate sample size or do power analysis for logistic regression with one nominal independent variable? Is there a way to do it with Stata?
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1answer
53 views

Sample size estimation for test for proportions

I'm interested in finding out if a particular activity increases the chance of a particular segment of prospects converting to a client. I would like to be able to detect a 5% difference in overall ...
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28 views

How should I calculate required n for minimum power of a sequence of parallel or simultaneous tests?

I am concerned with the practical situation in which I design a 'no-budget' split-ballot 2 x 1 experiment. We have money for $n=80$ cases in total, thus $n=40$ in each of two groups. In total I will ...
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13 views

Power analysis for environmental microbiology samples

In my experiment, I will be taking environmental samples in cheesemaking rooms of 20 dairy farms (each sampling point is a 10cm x 10cm square area that I swab and count the microorganisms I found back ...
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44 views

Required sample size with unequal variances

I have a setup with equal sample sizes ($N_1=N_2$) from two groups (sample means $\mu_1$, $\mu_2$), but different variances $\sigma_1^2$, $\sigma_2^2$ in both groups. If the variances were equal, ...
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12 views

Power of a case control test as a function of P(X=1) & P(Y=1)

For our course in statistics we had to build a simulation which would give insight in the power of a case-control study vs that of a cohort study, both trying to discover an association between 2 ...
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25 views

Binomial data: Null Hypothesis $p = 0$ when all Sample Values are 0 - testing and power analysis

I am trying to investigate if the proportion of successes in my population can be shown to be larger than zero. Thus, $H_0: p = 0$ and $H_A: p>0$. Since $p=0$, the prop.test in R does not work, ...
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11 views

relationship between power means and population zscore calculations

Can one use a power mean of the ages in a room to determine the age break down of a room? Let's say you have a room full of people, by using the average age and standard deviation of the age, how do ...
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1answer
66 views

Method to determine the sample size for a one-sample t-test

What method is appropriate to use for determining a sample size for one sample t-test? How can I conduct the power analysis in this case? I am looking for the analytical formula that would allow me ...
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1answer
35 views

Averaging effect sizes?

Suppose I need an estimate of effect size for a power analysis. I read the relevant literature and calculated Cohen's $d$ from some number (3) of studies. If the Cohen's $d$s are, for example, $d_{1} ...
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32 views

About multiple testing and power analysis

Doing a power analysis for a single t-test is relatively simple. What if I have to do several tests? If I were to use the Bonferroni correction, I could just take the significance level as 0.05 ...
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1answer
292 views

Can you calculate the power of a Kolmogorov-Smirnov test in R?

Is it possible to do a power analysis for a 2-sided Kolmogorov Smirnov test in R? I am testing whether two empirical distributions differ using ks.test(), and am looking to add a power analysis. I ...
2
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0answers
65 views

Power analysis for logistic regression

I have to deliver a statistical analysis plan that will have to be approved by an ethic commettee before I could start a clinical trial. I usually deal with different kinds of tests, whose power ...
2
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2answers
366 views

A priori power analysis: calculating sample size based on percentages

I'm trying to calculate the sample size, given alpha, beta resp. power, ...
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1answer
84 views

Power analysis for binomial test via simulation

Suppose a gene is mutated in 30% of the samples. I want plot the number of samples required to see 30% of them mutated at various level of power. I want to do this through a simulation so I ...
2
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0answers
424 views

Sample size and power calculations for a randomized controlled trial

I need help with the power calculations to determine the sample size of a randomized clinical trial. This is a relatively simple trial with two arms: an intervention arm and a control arm. Patients in ...
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88 views

Calculating sample size

I am going to conduct a research and would like to estimate the sample size that I will need. Here is the information that I have, please let me know if you need some more information. Thanks in ...
2
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1answer
222 views

Determining sample size for proportional hazard

I am in the design phase for a longitudinal study examining the effect of a predictor (neighborhood risk score) on time to an outcome (re-arrest), as well as whether or not the variation explained by ...
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1answer
81 views

Multiple regression a-priori analysis of power for sample size

I have used g-power and an online calculator to determine the sample size for a 2 factor regression but am unsure as to what effect size I desire as for a large effect size (.5) I only need 20-30 ...
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0answers
148 views

Deriving the power formula of the one-sample proportion test

I have to derive the power of the z-test in testing $$ H_0: \pi=\pi_0 \text{ versus } H_1: \pi>\pi_0 $$ Denoting by $p$ the sample proportion, the power equals $$ ...
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36 views

Can one manipulate data to demonstrate the power of the analysis?

I was asked this question about the demonstration of power. There are two groups of data, say control and treatment. If conducting a test( say a linear regression including other factors, but the ...
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0answers
27 views

One way between subjects ANOVA

I am planning to use a one way between subjects ANOVA to test for a difference of compassion between three different groups My question is how many participants would i need to collect data from and ...
2
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1answer
87 views

Power analysis on chi-squared test with low cell counts

I am hoping to perform a chi-square test of independence on data in a 2x2 contingency table with the following values: ...
2
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0answers
42 views

computing power in R

How can I compute the power of Dixon discordancy test in R. As there are functions for many other tests like t.test, ANOVA, proportions test etc. but not for this one. Any help will be warmly ...
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1answer
40 views

power for mixed-effects model

I wonder if there is a simple way of calculating an achieved power for a mixed-effects model. The fixed effects are the intercept and a slope. The random effect is for the intercept at the two levels ...
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0answers
28 views

DOE Power Calculation for Interaction Terms

I was using Monte Carlo to determine the a-priori power for the terms in a designed experiment. To do this I used the following procedure: Set an effect size I expect to see in my response Use the ...
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0answers
111 views

Sample size calculation - Pros and cons of using one-sided z-test over two-sample differences in means approach?

I'm calculating the sample size required for an experiment with continous outcome variable. I'm considering two ways to calculate the sample size. One is based on a differences in 2 means test. The ...
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0answers
28 views

Power analysis for AB testing— multiple variants

I'd like to do an experiment that is basically an A/B test with about 10 different conditions. A single trial results in either success or failure. The null hypothesis is that all of the conditions ...
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0answers
28 views

Determining the effect size using GPower

I have three ponds and would like to know how many random samples of algae I need to collect within each pond measuring 7 response variables. I would like to see how each pond responds to the 7 ...
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0answers
109 views

Using G*Power to determine the sample size for an repeated measures ANOVA

I am currently designing an experiment that I want to analyze using an RM ANOVA. Since some of the factors are confounded I need to do multiple ANOVAS. One analysis will be for 2x2 factors (within ...
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21 views

Cluster weights in PROC GLMPOWER

I am doing power analyses in SAS using PROC GLMPOWER to solve for a total sample size (N Total). I have clustered data (Ward method), to account for variability. There are 4 clusters of varying sample ...