Tagged Questions

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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56 views

Simulation of Monte Carlo test

Using R, I am trying to simulate how the power of a Monte Carlo two-sample test for central tendency changes with sample size. However, my simulation results does not show power increasing with sample ...
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1answer
32 views

How to calculate sample size for this study design?

I am trying to find out whether the number of participants I recruited (N=42) so far is sufficient for my study in which: there are two interfaces (say A and B). ALL students in the study will try the ...
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16 views

sample size power calculation

This is probably very simple but I am struggling...in a population there is a disease present clinically in around 35% of patients, we want to use two tests which when used in parallel have a ...
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17 views

number of participants/analysis

Hi I am really struggling here any help would be muchly appreciated, please use laymen terms where possible. research question: a comparison of quit rates between 3 smoking cessation treatments. ...
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33 views

Power calculation for a coefficient in linear regression

Consider a simple linear regression of the form: $$ Y \sim \beta_0 + \beta_1 X + \beta_2 Z + \epsilon$$ I have questions regarding calculation of power for $\beta_1$. To calculate power, I approached ...
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1answer
18 views

power to detect effect sizes for the usual t, Welch Adjusted t, and Mann-Whitney U test

For class, I am given a series of sample sizes and variances for two groups and am asked to calculate the power for detecting effect sizes for the usual t test, Welch adjusted T test, and the ...
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2answers
136 views

5 defectives rule of thumb

I have taught six sigma black belt classes using consultant sourced training materials which included the rule of thumb that when estimating the rate of occurrence of discrete events, like the ...
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1answer
25 views

What is the statistical power of a test when the true population mean is unspecified?

I have been given the following homework problem: To improve the reading scores of its students, a school district randomly selects 50 students to participate in a new program. The mean reading ...
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2answers
69 views

Empirical rejection rate of a wrong null hypothesis -is it the “power of the test”?

I guess this is basic, but it forms part of the holes in my statistics education. What I know is that the power of a hypothesis test is not a fixed magnitude, but a function of various factors ...
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2answers
67 views

Calculate necessary “treatment group size” for power in a regression setting

I have an observational quasi-experimental study, where I try to estimate the effect of a "treatment" (participation in a programme) on a continuous outcome. Participants (some two-thirds of all ...
6
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2answers
118 views

Example of an inconsistent Maximum likelihood estimator

I'm reading a comment to a paper, and the author states that sometimes, even though the estimators (found by ML or maximum quasilikelihood) may not be consistent, the power of a likelihood ratio or ...
2
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1answer
42 views

How to choose a Power and Alpha combination for a fixed sample size?

Let's say I have a sample size established with alpha=0.05 and power=0.8 (based on time constraint for study). The same sample size can be achieved with any of: ...
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1answer
309 views

Why is usually the acceptable probability of type 1 and type 2 errors different?

This question is raised by my supervisor and I don't know how to explain. Usually the accepted confident level is 0.95 which means that the probability of type 1 error is 5%. But the usually ...
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32 views

Calculate statistical power on groups with different size

Is it technically possible to calculate the statistical power for a test where the two groups don't have by design the same size. I'm thinking to a 90%-10% split of the population. Namely, is there a ...
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1answer
18 views

Increasing statistical power by having a highly sensitive outcome measure

Is it logical to say that you can increase statistical power by having a highly sensitive outcome measure? I say this because a highly sensitive test has low Type II error, and low Type II error leads ...
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1answer
41 views

When testing for a difference between effect sizes, is test power affected by their respective magnitude?

When comparing two effect sizes with a statistical test, does it matter for the test's power whether these effect sizes themselves are large or small? Imagine you are planning an experiment in which ...
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1answer
22 views

Effect of sample decimal points on power in rank-based tests

I perform different rank-based non-parametric tests (Friedman and Nemenyi) post-hoc and noticed that the decimal places of the samples have a strong effect on their power. Please consider the ...
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2answers
165 views

Post-hoc tests for MANOVA

I am using a MANOVA test to compare nine different dependent variables (from neuropsychological and neuropsychiatric assessment) between three groups. The output shows a significant influence from ...
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0answers
101 views

How to calculate post-hoc power analysis for multiple regression models?

I have few questions that came up while I was trying to calculate post hoc power analysis for a regression model: I calculated post hoc power analysis for a regression model that produced a ...
2
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1answer
82 views

Power analysis from Bayesian point of view

I was reading an article on a power analysis and sample size calculations for a class of models that known as joint longitudianl-survival models. The paper derives a closed form formula for power and ...
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2answers
88 views

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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29 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 ...
2
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0answers
33 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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18 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
109 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 ...
2
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1answer
175 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 ...
3
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1answer
41 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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0answers
82 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
23 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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0answers
29 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
26 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 ...
2
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0answers
105 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) ...
2
votes
1answer
41 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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2answers
82 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
136 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
62 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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0answers
48 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 ...
2
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0answers
27 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
79 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
36 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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0answers
15 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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0answers
113 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 ...
3
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0answers
65 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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0answers
33 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 ...
1
vote
1answer
37 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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votes
1answer
628 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
34 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. ...
2
votes
1answer
78 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 = ...
3
votes
1answer
433 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 ...
2
votes
1answer
247 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 ...