Is a property of a hypothesis testing method: the probability of rejecting the null hypothesis given that it is false, i.e. the probability of not making a type II error. The power of a test depends on sample size, effect size, and the significance ($\alpha$) level of the test.

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What does a post hoc power analysis say about the significance of the study results?

I orginially posted this over at AskMetafilter, and a commenter suggested I ask it here. I work for a dietary supplement company that also makes skin care products, and some of those skin care ...
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23 views

T-Tests and Regressions

my supervisor has asked me a few questions that I'm not entirely sure how to answer. For a quick summary, my study includes a small sample of 16. To describe the sample, I compared the scores of the ...
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0answers
23 views

power of poisson test with large sample size

I would like to compute the power of two distributions which are poisson with $n_1$ being large and $n_2$ being medium sized. I have used the formula given by Krishnamoorthy and Thomson for the C-test ...
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17 views

Statistics:Power Question Update [duplicate]

I have already asked this question but I did not initially give out all the details on the question, like the question being a multiple choice question. You manufacture and sell a iron rod whose ...
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1answer
91 views

Statistics: Power question

I have already answered this question I just like some feedback on am I right or wrong? You manufacture and sell a iron rod whose electrical conductivity is supposed to be 10.1. You plan to make ...
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1answer
24 views

Significant difference between proportions, found at sample size below that suggested by power analysis

I'm looking at data from experiments that have been run to look for a difference between proportions, 1-tailed. In many of these it has been found that there is a significant difference between the ...
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1answer
138 views

Statistical Power of ROC/AUC Test with non-IID Samples :: To how many IID Samples are my non-IID Samples Equivalent?

I've been assigned to solve the following problem as part of a serious, biological research project. I think I have a tentative solution, but I'm wondering whether the approach I've picked is the ...
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1answer
32 views

Power calculation; determine required difference in means

I want to perform a power analysis for a 2 sample t-test for the difference in means. However, instead of computing the required sample size, I would like to compute the required difference in the ...
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44 views

Logistic regression power analysis with moderation between categorical and continuous variable

I've been reading Simulation of Logistic Regression Power Analysis - Designed Experiments, http://sas-and-r.blogspot.com/2009/06/example-72-simulate-data-from-logistic.html, and Power analysis for ...
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0answers
12 views

Estimate power for linear model with Bernoulli-distributed error

I want to estimate a linear model for a phenotype $y_i$ defined by a liability threshold model, using observable data $x_i, c_i$. $$y_i = \mu + \beta x_i + \epsilon_i$$ $$\text{Pr}(\epsilon_i | x_i, ...
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25 views

power for estimating treatment heterogeneity in RCT

Could someone point me to a good resource for estimating power for detecting treatment heterogeneity via interactions in MR? Let's assume that individuals will be randomized to two study arms. To ...
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1answer
16 views

Comparing participant numbers in a systematic review

I am doing a systematic literature review on theories for measuring user satisfaction. I have to rate the quality of these theories, and one of the criteria should be the number of participants in the ...
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0answers
56 views

Sample Size Calculation for Cluster Sampling

I'm being asked to calculate a necessary sample size for a cluster sampling protocol. I don't have much experience with cluster sampling, so thought I'd come here. The situation is as follows: 1) ...
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1answer
39 views

Proportionality of significance and effect size

Is it true that, given a fixed sample size N, it can be said that some measure of effect size and the measure of statitical significance (e.g., 1-p) are proportional? In other words, that, when ...
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72 views

Increasing power of test by transforming format of data - is this cheating?

I'm working on a health care dataset that contains one row per member, measuring total number of the member's hospital inpatient (IP) visits during 2012 and 2013. The initial research question of the ...
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2answers
91 views

Power calculation of study using 2 sample z-test

This is not homework! I have two very different answers for a power calculation I have done on the below data - ...
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1answer
33 views

Can Inferential Statistics be carried out in a Retrospective Case Study?

Just wanted to check with regard to a retrospective case study, if various data is collected for a set of patients on different variables can this be interpreted with inferential stats tests? Even if ...
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30 views

Power Calculation - Calculation of Absolute Difference

I've been asked to undertake a power calculation because the regular statistician is not available. I am calculating power for a trial where the endpoint will be a percentage of patients not ...
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0answers
23 views

Noncentrality Parameter - what is it, what does it do, what would be a suggested value?

I have been trying to brush up on my stats knowledge, especially in relation to Sample size determination and Statistical Power Analysis. But it seems that the more I read the more I need to read. ...
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2answers
52 views

Power calculation for a test of trend over time

This paper (open access) Babies born at the threshold of viability: changes in survival and workload over 20 years (table 2) presents data for survival of extremely premature babies over the last 20 ...
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31 views

Relationship between statistical power and p-values

As you have an increase in statistical power, does this decrease the p-value? If so, why does this occur?
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13 views

Comparison test in unit root

I am not clear how to compare all the tests in Unit Root. Which one is the most powerful among: ADF PP KPSS Elliott, Rothenberg & Stock Unit Root Test
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58 views

Hypothesis testing simple null vs. complex alternative

This is a simple hypotheses testing question between a simple null and a complex alternative. I want to test the null hypothesis $H_0 : \mu = \mu_0$ against the alternative $H_1 : \mu = \mu_0 \pm ...
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0answers
39 views

How to run a power analysis for a repeated measures (all within-subjects) with combined contrasts?

I am looking for a little help on determining the correct way to run a power analysis on a within-subjects repeated measures design (i.e., no between subjects variable) with combined contrasts. ...
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28 views

Siginificant size for a Control Group

I am designing project which requires me to select a Control Group. One the business requirements stipulates that I select as small a sample size as possible for the Control Group so there will be ...
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1answer
34 views

Does power of a test depend on number of cases or number of observations?

Cases and observations. It is my understanding that sample size is determined by the number of individuals taking part in an experiment (from my undergrad Psychology stats course). For each ...
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1answer
270 views

What is the minimum viable cell size for 2x2 ANOVA?

I have a 2x2, between-subjects experimental design (2 independent variables (IVs) with 2 levels each) and one dependent variable (DV). My data are unbalanced and an interaction between the IVs seems ...
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1answer
29 views

Comparing fits in simulation for power analysis

I have the following data (just an small example here). I want to know effect of time and ecotype over height. ...
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1answer
64 views

How can you derive the sample size to obtain a particular type II error rate?

I often see that the sample size for a $z$-test to achieve a particular type II error rate $\beta$ (at a given significance level, $\alpha$) is: $$n = ...
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1answer
403 views

Why do I always fail to reject the null hypothesis on a binomial test for `p=.5`?

When performing a two-tailed test on a binomial process with p=.5, why are my p-values all over the place, and I virtually never reject the null hypothesis? I answered a question on stackoverflow ...
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1answer
132 views

Sample size function for McNemar test of repeated proportions in R

I have been scouring CRAN and Google for a function (that I wouldn't have to code myself) that would calculate the sample size needed for a pre-post design with a dichotomous outcome - to no avail. If ...
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1answer
122 views

Why does one report statistical power only when results are non significant?

It is well known that a study with low statistical power has a reduced chance of detecting a true effect. But if low power also reduces the likelihood that a statistically significant result reflects ...
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1answer
574 views

Is a priori power analysis essentially useless?

I attended a meeting of the Society for Personality and Social Psychology last week where I saw a talk by Uri Simonsohn with the premise that using an a priori power analysis to determine sample size ...
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2answers
212 views

R: power calculation for beta coefficient

I am interested in calculating the power for the beta effect size, for example ...
3
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1answer
135 views

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 ...
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17 views

Exposure in Power Calculations

When estimating power calculations for a case control study, what does exposure of controls really mean? I find lots of information how how to calculate exposure for cases when you already know ...
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18 views

Interpretation of results of power analysis with regard to the null hypothesis

I have recently read a paper, in which the authors conducted a $2*3$ Between-within-ANOVA. The alternative hypothesis was formulated with regard to an interaction effect, which did not reach the ...
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1answer
95 views

Power of t-test for aggregate data

I have data that have been aggregated with unknown variance into a number of composite averages. These data are generated from pooled assays, such as HIV viral load in a composite of 10 vials of ...
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2answers
156 views

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 ...
2
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1answer
79 views

Effect of dismissing data points in regression

I would like to know what is the effect of dismissing data points in a regression analysis. For example, say originally a sample of 100 data points is collected (say they are all useful, equally ...
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1answer
75 views

Why do these power functions for difference in proportions give different answers?

I am comparing two power functions in R, a base function stats::power.prop.test, and the function pwr::power.2p.test in the ...
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70 views

Minimum sample size for CART

What would be the minimum sample size for a CART analysis? I've found this recommendation: The original CART monograph discusses a study the authors performed working with 215 observations and ...
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2answers
368 views

Unequal sample sizes: When to call it quits

I'm peer reviewing an academic journal article and the authors wrote the following as justification for not reporting any inferential statistics (I deidentified the nature of the two groups): In ...
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1answer
349 views

Why the F-test in Gaussian linear models is most powerful?

For a Gaussian linear model $Y=\mu+\sigma G$ where $\mu$ is assumed to lie in some vector space $W$ and $G$ has the standard normal distribution on $\mathbb{R}^n$, the statistic of the $F$-test for ...
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0answers
21 views

Power analysis for log-gamma model

I fitted a generalized linear mixed log-gamma model in SPSS with 1 fixed factor (binary), patient ID as a random intercept and a continuous variable as (fixed) covariate. How can I calculate the ...
0
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1answer
44 views

Is there a way to measure the viability of an experiment?

Is there a way to calculate a number that evaluates the viability of an experiment? By that I mean the probability that the observed probability is just chance. I read about the $p$ value, but it ...
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1answer
188 views

Sample size calculation for a single proportion Without Any Comparisons (descriptive only): How to determine the margin of error in the formula?

I want to calculate the sample size for a single proportion (the prevalence of a disease). I know the formula and all: n = (z/m)^2 * P(1-P), where z is 1.96 (for 95% confidence level) and P stands for ...
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1answer
242 views

Power analysis of repeated measures ANOVA using simulation in R?

I would appreciate another opinion on this simulation approach to estimating power for a within-subjects (or repeated-measures) ANOVA; in this case a 2x2 factorial design. In other words, is there ...
2
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1answer
129 views

Calculating power function for ANOVA

There are several functions in R to calculate the power of a test, for example, the pwr-functions of the pwr package. My question is how we get this function for ...
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2answers
40 views

Undetermined power & retrospective study

My question is about a retrospective medical study in which no significant difference was found between two different treatments. What exactly is meant by "the lack of a significant difference does ...