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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0answers
20 views

Sample size and multiple comparisons problem on A/B tests

I'm running an A/B test in which we have 4 different messages on a landing page (the current one and 3 treatments/variations). My task is to determine the sample size for this test, based on a 5% ...
1
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0answers
17 views

Minimum detectable effect size for difference in difference estimator

This answer gives a formula for the minimum detectable effect size of the average treatment effect, given that the outcome variable follows a normal distribution, as follows: ...
0
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0answers
9 views

Affect of covariates on the power

I have calculated a sample size for some study. The response is binary, and there is one grouping variable, also binary. Now I am considering the addition of another covariate, and I wonder how will ...
1
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1answer
23 views

Computing required sample size for paired t-test

I have some paired t-test data (40 pairs) and I would like to use these data to estimate the sample size required if I were to conduct the study again with a new set of requirements. I'm using ...
0
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1answer
26 views

Sample Size for Multiple Testing

I want to calculate sample size for a classic multiple testing problem of multiple doses in clinical trials. I have 3 groups: "high dose", "low dose" and "placebo", and I wish to test if at least one ...
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0answers
3 views

Minimum Detectable Effect Sampling Weight

An experiment has two sub-populations, A and B, and I want to estimate a pooled intention to treat (ITT) effect $$Y_{i}=\beta_0 + \beta_1 T_i + \epsilon_i$$ where $T_i=1$ if treated in either ...
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0answers
9 views

Power Analysis Weighted Data

Suppose an outcome depends on the intensity of a treatment intervention $\pi$, where $\pi \in [0,1]$. Given intensity of treatment $\pi$, the data generating process is $$Y_i = \beta_0 + \beta_1 \pi ...
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0answers
43 views

Power of a Interaction term in R

I have analysed a dataset with a linear regression model, including an interaction term between a binary variable and a continuous variable. The interaction was significant. Afterwards, I have fitted ...
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0answers
28 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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0answers
34 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 ...
0
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0answers
30 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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0answers
19 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 ...
0
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0answers
21 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 ...
0
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0answers
42 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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0answers
39 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 ...
3
votes
2answers
125 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 ...
1
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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 ...
1
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0answers
13 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 ...
4
votes
1answer
101 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 ...
1
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2answers
41 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 ...
0
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0answers
74 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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0answers
33 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: ...
0
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0answers
69 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 ...
0
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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 ...
0
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0answers
25 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 ...
1
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2answers
79 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: ...
2
votes
1answer
59 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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0answers
45 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
58 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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0answers
38 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 ...
0
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0answers
15 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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0answers
47 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, ...
1
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0answers
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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0answers
27 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, ...
0
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0answers
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 ...
2
votes
1answer
73 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 ...
0
votes
1answer
39 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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0answers
33 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 ...
5
votes
1answer
347 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
votes
0answers
76 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
votes
2answers
495 views

A priori power analysis: calculating sample size based on percentages

I'm trying to calculate the sample size, given alpha, beta resp. power, ...
1
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1answer
102 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
votes
1answer
585 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 ...
1
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0answers
100 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
votes
1answer
306 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 ...
0
votes
1answer
108 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
170 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 $$ ...
1
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0answers
39 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
29 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
votes
1answer
96 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: ...