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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18 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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16 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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18 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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24 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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0answers
21 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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8 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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19 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
26 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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20 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
27 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
131 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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20 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
50 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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367 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
60 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
79 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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429 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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1answer
91 views

R: power calculation for beta coefficient

I am interested in calculating the power for the beta effect size, for example ...
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1answer
75 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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0answers
15 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
55 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
136 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 ...
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1answer
73 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
52 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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44 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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205 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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168 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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18 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 ...
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1answer
42 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
95 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
170 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 ...
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1answer
111 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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37 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 ...
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0answers
32 views

What is the Comparison p used in a sample size calculation for a 1-proportion test in Minitab?

In order to calculate a sample size for a 1-proportion test in Minitab, one has to input the power and the comparison proportion. Could someone provide a definition for the comparison proportion ...
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0answers
47 views

Noncentrality parameter in two-sample-t-test (Power analysis)

I am working with R, doing a post-hoc power analysis. Can anyone explain to me why these two commands generate different outputs? I thought they should not! ...
2
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1answer
59 views

Differences in power in regression versus mean of a ratio

I've been futzing around with the following example, and feel that there must be a good explanation or reference that I am blindly missing. Supposer you have a linear relationship between two ...
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0answers
17 views

Relationship between $H_{0}$, $H_{1}$ and the Power of the (one sided) hypothesis test

Suppose we wish to test$H_{0} : p = 0.5$ vs $H_{1} : p = p_{1}$ (where $p_{1} \gt 0.5$ What are the relative difficulties of testing for $p_{1}$ close to $0.5$ or $p_{1}$ far from $0.5$? I know that ...
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0answers
12 views

Adjusted-size in a Monte Carlo bootstrap simulation

For my thesis I computed various rejection frequencies based on p-values using various statistics based on the Wild Restricted Efficient bootstrap scheme of Davidson & Mackinnon (2010) by ...
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0answers
178 views

Power Analysis for repeated measures ANOVA

I am trying to run a post-hoc power analysis on a previously published report. The intent is to calculate the average obtained power for (the equivalent of) Cohen's effects of d = .20, .50, .80) for ...
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1answer
129 views

Question on calculating power for a prediction based study

I've calculated required power for a study in the past but I've come upon a scenario that I can't figure out quite how to do it. Pretty much I have a procedure that results in a particular ...
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2answers
84 views

Is the post hoc power of a dependant t test related to the sample correlation or actual correlation

I have a question that may be fairly easy to answer but it is making my head spin. If I do a paired t test on two groups of data with sample size 3 each AND I assume that the pairs are correlated with ...
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0answers
108 views

Power of McNemar Test

I have been playing around with the GPower tool to calculate the power of various statistical tests, and what I noticed is that if I can change the proportion of the discordant pair in the McNemar ...
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13 views

Real based on Power Function [duplicate]

Problem: What is a real life example of a power function? I tried thinking about it but I failed. Does somebody know?
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1answer
82 views

Power analysis for biased coin in R

I have an experiment where I'd like to determine if a coin is biased. I'm using the binomial distribution to look at coin flips. I've collected data from a sample of 30 flips and found that in 24 of ...
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1answer
264 views

How do I do an a priori power analysis for a 2x3 factorial anova?

Apologies if this is confused, I'm utterly lost with this. I want to do a questionnaire based experiment with 6 conditions (1 factor with 2 levels and another with 3 levels) and different participants ...
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1answer
90 views

How is power for t test and Mann Whitney comparable when null hypotheses differ

In a previous question, I asked about comparing the power of a t test to a Mann Whitney test under different situations. One of the answers pointed out that the worst that the Mann-Whitney can ever ...
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2answers
225 views

Power of a Mann Whitney test compared to a t test

So a Mann Whitney U test is supposedly about 95% as powerful as a t-test when t-test assumptions of normality and homogeneous variance are satisfied. I also know that a Mann Whitney U test is more ...
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0answers
40 views

Appropriate way to estimate sample size requirements for an unknown population distribution

Assuming we have a sample (some observables) from a population of unknown distribution, can I assume that the right way to estimate the sample size (for estimating means, medians, etc.) is using the ...
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0answers
26 views

Sampling from dataset without sacrificing power of multivariate logistic regression

I'm developing a multivariate logistic regression model for a large healthcare dataset (100 million+ rows of demographic and diagnosis columns) where the event in question, an inpatient admission day, ...