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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6 views

a priori power analysis for ANOVA plus post hoc test

I would like to perform an a priori power analysis to calculate required sample size for data to be analyzed using one way ANOVA and Tukey HSD post hoc test. (Or simply apply Bonferroni correction). ...
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20 views

CFA power analysis using existing Likert-type data with lavaan and simsem in R

To preface, this is my first foray into CFA and SEM, so please forgive me as I am likely making a number of unwitting mistakes. I am currently working on a study to validate a proposed psychometric ...
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16 views

Determining sample size using power analysis in multiple testing context

I am currently trying to determine the required sample size for an experiment. As I want to use the statistical power concept (for a t-test) to determine the required sample size, I want to specify a ...
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25 views

Unequal Sample Size Effect on Power Calculation

I am new to power analysis and have been experimenting with one-way fixed effects Anova in G*Power (Fixed effects, omnibus, one-way). 1) When dealing with unbalanced design, the effect size is ...
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22 views

Different sample sizes, skewed data and unequal variances

I am a bit confused regarding best statistical test to use for my data. Here is the details: I did a study to compare two independent groups; 31 patients and 60 healthy controls. I have around 50 ...
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13 views

Multilevel Power of a Mixed Model

For my dissertation I have data from 57 employees that responded the same survey on 11 occasions (i.e., 11 observations per person for each variable). All variables I am interested in (and are ...
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4 views

Power analysis for two-sided non-compliance

Using Chamber of Commerce data for a small town, a local non-profit wants to evaluate the effectiveness of direct mail vs. email for getting business owners to contact the non-profit. We aren't ...
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9 views

Power calculation - categorised continuous exposure in case-control study

I have a continuous exposure that I would like to catagorise it into quantiles according to the distribution of control (i.e. 25% controls in each exposure level group). From pilot study, I know that ...
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1answer
29 views

Why does R power.prop.test & R prop.test show inconsistent results?

I am a bit confused by the differences I am seeing between R's power.prop.test & prop.test functions. To estimate the sample size needed for an A/B test I am conducting I am using the following ...
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1answer
42 views

Is there any conventional small, medium and large effect sizes for ordinal logistic regression?

I was performing a power analysis of articles published in a journal of management using the pwr package in R. However, it seemed to be impossible to compute power ...
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26 views

Interpreting pvalue in the light of known power

I'm puzzled with the interpretation of a pvalue in the light of known power Let's say I study the association between a dichotomic variable (a treatment) and a quantitative one, which is my primary ...
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1answer
32 views

number of participants to have a 80% chance of detecting a 1.5% point difference as significant

Can someone explain how the math used to determine that 34 participants were required for this study? To have an 80% chance of detecting a 1.5–percentage point between-group A1C difference as ...
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13 views

Best way to calculate power, precision & sample size using complex pilot data set?

I have a large and complex pilot data set of electromyographic (EMG) data collected from human subjects performing several different exercises. A single subject was used for all data collection in ...
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1answer
18 views

What, if anything, is the relationship between random intercepts models and compound symmetry?

In the analysis of correlated data, you're often working with replicates where a worker does a task 2 or 20 times, or an individual is measured for blood pressure randomly over several times during ...
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14 views

Is Mann Whitney U test appropriate for samples of really different sizes and distribution?

A Mann-Whitney U test on two samples of different sizes (Group A: 170,000) Vs. (Group B: 200), different distribution shape (as per Kolmogorov-Smirnov Tests ks.test ...
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10 views

Power calculation for panel regression

How do you perform a power calculation in a panel regression setting? In particular what do you use as your sample size. The number of individuals or the number of observations (individuals x time ...
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1answer
24 views

Measures of minimal detectable effect size

Statistical power is defined as the probability of wrongly accepting the null hypothesis for a given sample size, p-value cutoff and effect size. I am after accepted measures of the converse: the ...
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16 views

Power analysis for polynomial regression

There are two variables, $X$ and $Y$. I am interested in the shape of the relationship between $X$ and $Y$, specifically whether it is linear, curved, or some higher order polynomial function, because ...
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20 views

GAM or spline power analysis in R

There is a package in R called pwr. This is useful to make power analysis when designing the sampling of a project. here are few examples: ...
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1answer
402 views

How to find correlations between multiple low-frequency variables?

Let's say we have multiple ($k > 2$) binary variables (e.g., genetic mutations and/or disease states), which appear at a given frequency of $f(1)$ to $f(k)$ in a sample. We would like to test ...
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1answer
34 views

Some questions on multiple logistic regression

Let's say we have k binary (binomial) variables, and a sample size of n observations per variable, where each variable occurs (positive case) at a given frequency/probability f. We would like to check ...
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1answer
67 views

Power calculations Uniform(0,$\theta$)

I am working on this problem and got about halfway through it, before getting stuck. Could anyone take a look at it? here's my problem... $x_1,...,x_4$ are distributed $U(0,\theta), \theta>0$ ...
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81 views

Power Analysis By Simulation

Background: We have a developed an alternative website which we believe will increase sales by a small percentage (1-4%). Although small this is very valuable. Our Site: Visitors are tracked by a ...
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2answers
37 views

Statistical power of binomial vs. paired t-test

I am conducting an experiment and I am deciding whether to use a forced-choice paradigm (participants choose A or B), or a continuous rating paradigm (rate each stimulus A and B on a Likert scale). ...
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33 views

Barnard's Exact Test (Boschloo's variant) when distribution is hypergeometric

Let's say, we have a standard $2 \times 2$ contingency table and because of low sample size we're about to use some type of Exact Test, e.g. Fisher's Exact Test (FET) or Barnard's Exact Test. It's ...
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28 views

Determining the power associated with the logistic model

Although there has been some detailed discussions about power analysis on this website (for example here and here), the answer provided to this question has outlines the steps to simulating a power ...
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18 views

How to determine statistical power when I must use Welch's Robust Test of Equality of Means

I couldn't use a one-way ANOVA on my means comparisons (3+ groups) because I have heterogeneity of variance (and unequal group sizes), so I used Welch's Robust Test of equality of Means. Of all my ...
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13 views

Combination of Tests' Power

I have set of tests. It is not difficult to calculate power for each of them (I have normal distributions and know effect sizes). I would like to infer power of combination of tests. I.e., $H_0 = $ ...
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8 views

guidelines for repeated measures anova power

I has been requested to assess the power of a repeated measures analysis experiment: 11 subjects, one between subject variable (product, three levels) and one within subject variable (time, four ...
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19 views

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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24 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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12 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
130 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
38 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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25 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
87 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
18 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
14 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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22 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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11 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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13 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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12 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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23 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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18 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
238 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
37 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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23 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
38 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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37 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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30 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 ...