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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Power Analysis for Within Subject ANOVA

I am going to be collecting survey data that asks for participants' attitudes towards four groups of people. For the sake of this example, let's say that it's black women, black men, white women, and ...
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14 views

Which version of Barnard's exact test to use?

Everything starts simply, we have standard $2 \times 2$ contingency table and we're determined to use Barnard's exact test over Fisher's exact test due to higher power. And here, the question arises: ...
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16 views

Determining sample size of skewed data

I have seen questions asking about sampling with non normal data but did seem to help. I have two datasets, dataset A containing results of students before ...
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8 views

Clustering and power: increasing the n but not the number of clusters

I am designing an experimental study with N observations from M sampled clusters, where M << N. Half of the clusters will be assigned to treatment. I can spend more money to increase the number ...
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2answers
64 views

Post hoc power analysis for a non significant result?

I have submitted a paper to a journal reporting a non-significant finding. One of the reviewers has asked me to include a power analysis on my data to work out how big a sample size I would need to ...
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1answer
33 views

What do they mean by 'To calculate sample size, I use simulation in all cases.'?

I was looking for a book on sample size calculations and power analysis and I met this phrase 'I use simulation in all cases.'. What does it mean, can i forget about using traditional methods for ...
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19 views

Minimum sample size for 1-tailed hypothesis testing

Let's say we have some endangered species of animals, whose population is 10,000 and dwindling due to some disease they all carry. And say I want to be able to test the efficacy of some new drug (with ...
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1answer
44 views

How to draw the estimated power curve of a test?

The estimated power of a given test can be reported with a table or with a curve in a plot. I need to compare the power of two permutation tests by simulation and I was wondering how to create a ...
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1answer
12 views

converting a chi-square with more than one degree of freedom into a pearsons r

I want to run a power analysis for a study using correlations between two continuous variables. Previous research with the variable I am interested in used a Kruskal-Wallis test to look at differences ...
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2answers
10 views

Prospective power using observed difference

In my line of research we often calculate prospective power of a proposed study as a way to determine what sample size we should aim for. However, I'm often studying phenomena, or interactions between ...
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16 views

Power of a binomial based test

I have a Bernoulli trial, which by definition can be either success of failure, and I have a Binomial random variable of the number of successes, where I don't know p (I wish to estimate it). I have a ...
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10 views

Power calculation for assessing relatively success two different predictors on a continuous outcome, Fisher r-to-z?

I'm thinking about a study where I assess the relatively predictive power of two different measures. Let's say a patient comes to a clinic on 3 different days, and 3 different measures of a noisy ...
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12 views

Help with Power analysis with PASS

I'm putting together a Power analysis, which is not my strong suit. I'm using the Poisson Regression tool in PASS. My outcome variable is falls over a five year follow-up period. My exposure is a ...
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0answers
11 views

Why is a larger sample required for a weaker rate when the response is a binary event?

I am interested in conducting an experiment and am attempting to calculate the sample size required for this experiment. If I hold beta at 0.8, alpha at .95, and am looking for a 5% increase, why do I ...
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0answers
21 views

Determining the number of operators (random effect) for a two-way chi-square test

I am designing a study to benchmark a new measurement technique with two traditional measurement techniques. Let's call the new technique N and the two traditional techniques T1 and T2. It is believed ...
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17 views

Statistical support to aid setting weights in a simple function

I'd like to create some consensus scoring function that incorporates two independent scoring functions $f_1$ and $f_2$. These functions rank items $i$ where there are $i=20,000$ items. $C_i = (f_1 ...
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1answer
218 views

Consequences of exceeding sample size after determination of sample in power analysis

Challenge In our office, I have been involved in a discussion about sample size and its influence on effect size - can you help me out and explain further? Base When conducting a power analysis, ...
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1answer
30 views

Power calculation using simulation — should I use empirical distribution?

In most tutorials on power calculation using simulation (e.g. this example in R), the analyst simulates the outcome variable using some convenient distribution such as the normal distribution. It ...
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0answers
18 views

Inflated Type 1 error in glmer (for main effect but not interaction?)

I am doing simulations of type 1 error, power, and power' (power corrected for anti conservativity) for research on a specific application of (g)lmer, namely to small-N designs of longitudinal ...
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1answer
34 views

Can increasing the significance level help to avoid detecting minor differences in large datasets?

In the accepted answer of THIS question, it is stated that "With such large sample sizes both tests will have high power to detect minor differences". On the other hand, a voted up comment in THIS ...
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36 views

How do I calculate the N to achieve a given precision for a binomial with parameter p?

I want to find out the prevalence of tuberculosis in patients coming to hospital with acute respiratory infection. What should be the sample size that will be needed given a precision of 5% with a ...
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0answers
23 views

Power calculations with a continuous independent variable in a case-control study with pair-matched data

So I have been struggling with this matter quite a while now and still have not found a solution to this problem. In fact similar questions have been asked here before but no answer was provided to my ...
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0answers
17 views

standard error for proportions from a bootstrap sample

I am trying to estimate the power (with confidence interval) of one-sample $t$-tests (with sample size $N$) on a parametrized distribution. One approach is to draw $N\times K$ samples from the ...
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27 views

How to calculate the required sample size?

Basically I am looking to see if a resistance to a certain drug is associated with a higher level of plasma protein. Resistance is a" yes or no "variable and the plasma protein is a nominal value. ...
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7 views

Power Calculation for Gene Significance

So, I think I need to do a power calculation for the following, but I am really not sure if that's the right procedure to use: I am looking at gene types in cancer, and I want to figure out if ...
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11 views

Accounting for time series correlation in power calculations

we want to do power calculations for a clustered RCT design household survey. We have a good idea for cross-sectional ICC from a similar earlier survey in the same study area. However, this time we ...
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1answer
91 views

Power analysis for a multinomial logistic regression

How do I conduct a power analysis for a multinomial logistic regression analysis? I have 1 independent variable (with 3 levels) and 1 dependent variable (with 2 levels). All variables are continuous. ...
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0answers
8 views

Is my loss of power in a combination study expalinable by estimating two GEE's?

I currently try program a combination test for longitudinal data and I am currently using GEE in R for that. I have a reliable sample size formula that gives me the desired power of 0.8 when I do that ...
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1answer
78 views

Power analysis for inter-rater reliability study (Kappa) with multiple raters

I've spent some time looking through literature about sample size calculation for Cohen's kappa, and in several studies there are stated that increasing the number of raters, reduce the number of ...
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0answers
18 views

Sample size for variable selection methods?

I have data in which the response variable is occupational injury rates ( positive continuous variable), and the predictors the job characteristics (standardized on a rating from 0 to 5) which might ...
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0answers
35 views

Why does significance not equal validity? Why can't I stop a test as soon as it has significant results?

According to this article, there's an issue with concluding a test as soon as it reaches significance (the "peeking effect"). Instead you need to determine the sample size ahead of time, and only look ...
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0answers
7 views

How many raters do I need to determine reliability of agreement on stimulus classification?

I have a stimulus set comprised of 147 videos, each with one of seven labels (hidden from raters). I want to determine how reliable label assignment is for each stimulus -- that is, I want to be able ...
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0answers
47 views

Sample size for A/B testing

I'm using Evan Miller's sample size calculator as well as his article "How not to run an A/B test". In my case, I'm using a conversion rate of 6.3 with a minimum detectable effect of 5% (that is, ...
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0answers
36 views

Power in survival analysis

I just read an article discussing the effect of radiotherapy duration on survival. They state the following: It was expected that changing the treatment from 1 week to 3 weeks would improve ...
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16 views

Power calculation to test different intercepts in simple linear regression

I have two groups of data: patients and healthy controls. I perform a measurement and a modelled estimation of this measurement on both groups. I then calculate using simple linear regression ($y = ...
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40 views

How to calculate effect size using minimum clinically important difference in sample size calculation for one way ANOVA test

I am doing a sample size calculation for a one way ANOVA test with four groups. The type 1 error level is alpha=0.05 and required power is 0.8. The standard deviation within each group is estimated as ...
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0answers
19 views

Expected significance level (alpha level) for a binomial glmm using glmer()

I have data on a investigation with only three real replicates. However I have repeated measurements, that probably improve the power of the analysis. Since my response is proportional data I use ...
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0answers
48 views

Is population homogeneity applicable to binomial parameters?

Are there assumptions regarding homogeneity in power calculations and significance tests when it comes to binomial parameters? Binomial variance is estimated by np(1-p). It doesn't take any other ...
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0answers
24 views

Sample sizes and power values in logistic regression analysis

I would like to perform a power analysis for a univariate logistic regression model in the case of a continuous regressor. I performed an analysis in R using ...
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0answers
10 views

Performing a power analysis for a cross validation study using C-test

I would like to perform a power analysis for a cross-validation study (training test 1:2) using C-statistics. When it comes to power analysis for to or z test I use G power software but I am not sure ...
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44 views

Power Analysis for Correlation-coefficient

From a prior study, a correlation coefficient of 0.9 was achieved with 16 experiments. Each prior experiment consisted of 10 to 300 subjects. From going through StackExchange posts I understand sample ...
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52 views

Sample size calculators

Background: I understand the formulae and manipulations below. My question refers much more to rules of thumb for which I have very little knowledge or experience If I were to build a sample size ...
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0answers
13 views

Fisher Test power

I have a 2 by 2 contingency table, and I want to do a two-tailed fisher test. I have sample sizes n1 and n2 constrained, but how does one decide the two probabilities you can test for? For example, I ...
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0answers
19 views

Are there dangers in inference when collecting additional samples in descriptive research?

I recognize that, for hypothesis testing, collecting additional samples after the fact present additional researcher degrees of freedom, and break several of the key assumptions we have in ...
2
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1answer
48 views

Proper interpretation of statistical power for 2 proportions

I have test results from 2 suppliers. 20 samples from Supplier 1 resulted in 8 units passing a test and 12 units failing; a failure proportion of 0.6 20 samples from Supplier 2 resulted in 2 units ...
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34 views

Sample size calculations

Suppose I have a set of 5,000 proposals submitted to a competition for funds. After review 10% were Rated Highly, 15% Average, 75% Poor. I want to take a sample from the group of proposals and test ...
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0answers
36 views

Categorical Variables With Little Variation. Chi-Square Test Power

Suppose you are trying to determine whether there is an association between gender and a rare disease, I suppose using the Chi-Square test. My intuition tells me that you must observe so many men, ...
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0answers
8 views

How can I calculate sample size for repeated measures one-way ANOVA using R? [duplicate]

I will be performing an experiment of 3 levels across one factor, and analysing the results using a repeated measures one-way ANOVA, using R. Before starting the experiment, I want to perform a power ...
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16 views

What probability to select in calculating Bayesian power?

I am comparing a Frequentist to a Bayesian test, running many simulations of the experiment. I want to compare the power of both tests, assuming the Null is true. For the frequentist test, I can ...
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95 views

how do i calculate sample size for ANCOVA?

I have two IVs and one covariate. How do i calculate my sample size. I'm not sure how to use the gpower software too. your help is greatly needed. thx.