Tagged Questions

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 ...

43 views

Simulation of random-effects meta-analysis yields biased tau^2

I need to realistically simulate study effect sizes and within-study variances for a random-effects meta-analysis in which the outcome is a relative risk. My question: why does this simulation lead to ...
13 views

Calculating “sample size”/power when I already have a group

I am doing a project on carpal tunnel syndrome. I am looking at electrophysiological and symptomatic data before surgical intervention and again afterwards to assess whether symptomatic relief ...
23 views

Logistic regression: high proportion of events

I am trying to calculate a priori sample size for a bivariate logistic regression with 9 covariates (some categorical; some continuous). My problem is that I have a high proportion of events to non-...
74 views

Calculating Power Z*score

I am trying to present sample size determination based on determining a certain difference between two proportions and the power of the test. As I understand it, my calculation requires both z-alpha ...
27 views

Power analysis in structural equation models

I’m getting different estimates when estimating sample size for a structural equation model when I use different utilities online. How would you calculate the sample size a priori for such a model?
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How to calculate the power of my quantile regression model?

I have a quantile regression model that I fit with the rq() function in the quantreg package ...
16 views

How does imputation affect significance test power?

There are many different imputation methods that make different assumptions about the missingness of the data (MCAR, MNAR, MAR). Since this assumption may not be met, I'm interested in knowing how the ...
10 views

Power Analysis for 1-sample Longitudinal Observational Study

I need to calculate the minimum detectable effect given a known N and desired power. I have a CONTINUOUS EXPOSURE and continuous outcome, each measured twice (baseline + 1 follow-up). If possible, I ...
6 views

what is the difference between generalizability theory and power analysis

Genearalizability theory, especially the decision study(D study), sounds very similar to Power analysis. A D study uses the variance components from previous variance composition of the measurement ...
42 views

Calculating power of a sample (need a layman's/beginner's definition)?

We have a bi-annual survey and an intended sample size of 1,300. This sample size was determined using Krejcie's means formula for finite populations, and we drew the sample using 2-stage clustering. ...
19 views

G*Power post hoc power analysis , unequal sample sizez

I am conducting post hoc power analysis using G*Power. The test conducted was Anova, fixed effects, one-way, with one control and two test groups. Control had 25K records, each of the test groups had ...
24 views

Sample Size Formula for Wilson Score, Clopper Pearson, and Jeffrey's

I am interested in finding the sample size formulas for proportions using the Wilson Score, Clopper Pearson, and Jeffrey's methods to compare with the Wald method. Also if anyone has code to replicate ...
7 views

Parameter recovery study for a computational model: assessing model slopiness and practical implications

Consider a decision-making computational model with 6 free parameters. The model mimics human behavior: for a given decision-making task, it generates decision times and accuracy. For each parameter, ...
49 views

Linear mixed model with repeated measures sample size

I have a pilot study about testing 2 drugs and a control (placebo) to see which drug is more effective. The design is as follows: Drug 1 is given to 5 random people then the response is measured 5 ...
51 views

Estimation of the probability of the winner's curse

The increase in false-positive results arises primarily from an overestimation of effect sizes, leading to upward-biased effect sizes that often cannot be reproduced in follow-up studies (‘the winner'...
36 views

Power Calculations using “Percent Change” vs. “Absolute Values”

Percent change can be extremely misleading for a number of reasons (e.g. regression to the mean), even though in the medical literature percent change is used quite frequently to "normalize" clinical ...
36 views

How to perform a power analysis in this case?

I want to know how to perform a power analysis in the following case to know if my sample is good enough or not. In my faculty, we have decided to apply a new lecturing methodology to a set of ...
7 views

Formula to convert test-retest reliability into SD of difference

Wanting to work out the statistical power of a repeated-measures t.test. This requires an estimate of the SD of differences within pairs (the correlation between measures for a given person is what ...
33 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. (I want to determine pair-wise which ...
51 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 ...
26 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 ...
60 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, Post hoc power). When dealing with unbalanced design, the effect ...
39 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 ...
18 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 ...
9 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 ...
17 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 ...
35 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 ...
55 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 ...
33 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 ...
41 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 ...
24 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 ...
21 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 ...
25 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 ...
15 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 ...
32 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 ...
20 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 ...
26 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: ...
409 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 ...
40 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 ...
73 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 $U(0,\theta), \theta>0$ ...
86 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 ...
45 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). ...
38 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 ...
33 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 ...
26 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 ...
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., $H_0 =$ ...
12 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 ...
27 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 ...