Effect size is "a measure of the strength of a phenomenon or a sample-based estimate of that quantity" [Wikipedia].

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Determining the effect size using GPower

I have three ponds and would like to know how many random samples of algae I need to collect within each pond measuring 7 response variables. I would like to see how each pond responds to the 7 ...
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106 views

Why do irrelevant regressors become statistically significant in large samples?

I am trying to better understand statistical significance, effect sizes and the like. I have a perception (perhaps its wrong) that even irrelevant regressors often become statistically significant in ...
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39 views

Which method should I use to combine the data of my studies?

I want to make a meta-analysis on household consumption expenditures elasticity data. In these studies that I've got; methods and regions and etc. varies according to studies. But at last, the results ...
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33 views

Effect sizes (eta-squared) with confidence intervals for linear models

STATA has recently implemented effect size calculations for regression models in their postestimation procedures measures of effect size in Stata 13. It takes a regression or ANOVA object as input, ...
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36 views

R code for standardized coefficents and model effect size using nlme

I have fit a longitudinal random effects model using nlme and I prefer nlme because I can get p-values. While working with a ...
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2answers
47 views

Statistical significance versus sample size [duplicate]

Statistical significance of a (variable in a) model grows with sample size. Citing Gilbert (1986): If one uses test statistics with constant size (i.e. a constant degree of confidence), almost any ...
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61 views

Effect size to Wilcoxon signed rank test?

Some authors (e.g. Pallant, 2007, p. 225; see image below) suggest to calculate the effect size for a Wilcoxon signed rank test by dividing the test statistic by the square root of the number of ...
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1answer
43 views

Can you add up effect sizes of two related variables (e.g. age + age$^2$) from a single regression model?

I am interested in the effect of age on outcome Y. I have two nested linear regression models to test linear and quadratic effects of age: Y= $\beta_0$ + $\beta_1$ some_covariate + $\beta_2$ Age + ...
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1answer
51 views

What measure of effect size in ANOVA has mode at zero under the null (unlike $\eta^2$ that does not)?

I encountered a weird effect when computing eta squared in ANOVA. Here is a short simulation to demonstrate it. I simulate $k$ groups with $n=10$ each, with all values drawn from standard normal ...
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18 views

Is there any possible method to calculate effect size in SPSS mixed model?

I run MIXED command for mixed model analysis of repeated measured data. However, there is no option or menu for estimate power(like partial eta in GLM) in mixed analysis. Is there any method to ...
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27 views

Multiple Regression - effect size

I want to calculate the effect size of a multiple regression. So far, I used Cohens f^2. Somehow, I wonder, if the effect size expressed by Cohens f^2 is an appropriate measurement. Let's assume ...
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125 views

How to test difference between standardized difference between means

On a data set I inherited, I calculated the standardized difference between the means of 2 groups, d, for each of 5 variables. All the data was collected from same set of about 175 people, with 35 in ...
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28 views

meta-analysis, effect sizes for standard deviations

Is there any possibility to calculate effect sizes for the differences of standard deviations of two groups? (Is there any possibility to calculate the difference in the standard deviation between two ...
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33 views

Can I calculate effect size using only % difference between means?

I need to calculate the effect size of a published experiment so that I can compare it to a replication attempt. However I have very limited information about the original experiment - only the mean ...
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44 views

When an effect size has to be considered sufficiently large?

I submitted a paper in which I analyzed the data by a mixed design ANOVA. I reported generalized eta squared as effect size. After significant interactions, I conducted planned comparisons. A reviewer ...
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13 views

Mixing ITT and TOT/LATE Effect Sizes in Meta-Analysis

I have a question concerning the coding of Effect Sizes for a large (educational) Meta Analysis with mostly latent outcome variables. Some studies provide "Intent to Treat" Data from which I ...
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1answer
35 views

Compare two distributions of large sizes and unequal variances where one distribution is heavily skewed

My data is from cells that are treated under two different conditions and then their response to the condition is measured by one output variable. The cell populations in the two conditions are quite ...
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16 views

Compute effect size based on simulation using different lists of different length

For my research purpose I wrote a small simulation to compute an empirial p-value based on an input gene list and a reference gene list. The idea is to check for each gene in the input gene list, the ...
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35 views

Definition of $\lambda^2$ effect size measure

In an article in the American Psychologist there is a series of bar graphs with a statistic next each bar. The statistic is described in the text and in the graph captions as being an effect-size ...
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1answer
250 views

Mann-Whitney U-test: confidence interval for effect size

According to Fritz, Morris, and Richler (2011; see below), $r$ can be calculated as an effect size for the Mann-Whitney U-test using the formula $$ r = \frac{z}{\sqrt N} $$ This is convenient to me, ...
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32 views

How do I convert Cramer's V to Cohen's d?

Say I have a chi-squared test that compares 3 different groups: $\chi^2_2 = 9.81$, $p=.012$, Cramer's $V=.33$ How would I go about converting this to a $d$-statistic? Is the proper approach in ...
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24 views

Can Hedges' d be used to compare unlike effects?

I've got a question related to the use of Hedges' d in a meta-analysis of insect fitness information. Here is a link (pdf) to the paper I'm working with. In the appendices, the fitness information ...
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14 views

Effect size for hypergeometric test

Given an urn with N genes, ugh - I mean with N balls, B of which are white, I can calculate the probability of randomly drawing b or more white balls in a sample of n using hypergeometric test. This ...
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1answer
17 views

problem: a sample size for the assumed effect in the 2 sample proportion test

I would like to calculate a sample size for the 2 sample proportion test when the significance level is assumed (0.05), power is assumed (0.90) and I'd like 2 sample proportion test to detect that ...
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21 views

Non-parametric effect size

Effect size, as estimated by Cohen's $\delta$, is: $d=\frac{\hat x_1 - \hat x_2}{\hat s_{pooled}}$ Since the numerator is an estimate of difference in location, and the denominator is an ...
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301 views

How to use delta method for standard errors of marginal effects?

I am interested in better understanding the delta method for approximating the standard errors of the average marginal effects of a regression model that includes an interaction term. I've looked at ...
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18 views

Statistical comparison of 2 dependent cohen's ds

How would I statistically test the significane of the difference between two Cohen's d derived from different tests within the same sample? Specifically, in my neuroimaging data metabolism in brain ...
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1answer
50 views

Effectsize difference between Mann-Whitney U and t-Test

I have data that is officially not normally distributed (Kolmogorov-Smirnov test < .000 BUT N=around 1200 so K-S not really reliable). In plot I can see that form looks good but negatively skewed. ...
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2answers
155 views

Effect size for a one-sample t-test

Imagine I work in a screw factory (which is not true). We have been producing a series of 5cm-long (on average) screws for years. I want to modify the production parameters in order to save some money ...
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1answer
39 views

Effect sizes for post-hoc paired comparisons in one-way ANOVA

Is there any alternative (like Cohen's d in t-test) to report about effect sizes for post-hoc paired comparisons in a one-way ANOVA (3 factor levels, correlated samples)?. Many thanks!!
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1answer
119 views

Interaction terms and effect sizes in multiple regression

I know there are similar questions on here, but I can't quite find an answer that covers all of what I need. I am running multiple regression in r with two predictor variables and sometimes an ...
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1answer
322 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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66 views

Effect sizes in within-subject design on R

I'm doing a meta-analysis but I need your precious help on couple things : 1) First, on R, in the compute.es package, I found only effect sizes computation formula ...
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1answer
53 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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134 views

How to get proper effect size from LMM?

I now have a problem with effect size of LMM. Someone insisted that I should have effect sizes after p values. I then thought that I can use 'estimate' in the output of pairwise comparison using ...
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1answer
23 views

How are these negative values understood?

I can't find literature to understand this table. What I know doing my research is that an effect size should be between 0 and 1. when 0.2 is slow, 0,5 medium and 0.8 and higher , high. But In an ...
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34 views

Mann-Whitney U test [closed]

I am comparing 2 separate datasets with the Mann-Whitney U test. I am analyzing three separate parameters present in both datasets and want to know which parameter gives greatest separation between ...
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1answer
81 views

3 way mixed ANOVA & pairwise comparisons effect size

I have a 3 way mixed ANOVA, where I have 2 significant main effects, one significant two way interaction and a significant three way interaction. I've been told to not describe the lower order ...
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1answer
112 views

Calculating effect size (partial eta squared) for a planned comparison effect

I have a between-subjects ANCOVA (factors A and B, and covariate C), for which A*B is significant. I decomposed the interaction with a planned comparison described by the contrast A=(-1,1), B=(0,1), ...
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1answer
144 views

How to perform a meta-analysis of studies without a control group?

I want to meta-analyse some studies which I've already collected and review. However, the studies did not used control groups, due to the types of questions used. How can I do the meta-analysis or ...
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64 views

Is there an effect size for Kappa's?

I am staring a project on comparing standard ways of creating a classifier with some heuristic methods. The heuristic methods should result in a faster training for the classifier but should result in ...
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26 views

What is a “concordance score” for regression coefficients?

I came across this "concordance score" in a set of slides called Penalized regression methods for ranking variables by effect size, with applications to genetic mapping studies, by Ji Zhu: $$ ...
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3answers
61 views

Does the order of magnitude of sample values influence p-values and effect size?

When using an independent-samples t-test to compare two variables, do the absolute values of the samples affect the test statistic and the effect size? In other words, is it easier to obtain ...
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51 views

Statistically correct to compare two Spearman's $\rho$-Vaules?

I have different variables (A, B, C, D) which are all ordinal scaled. I have another variable (Z) which is ordinal scaled, too. My sample size is approx. 1.500. Is it in the statistical sense ...
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3answers
272 views

Calculating effect sizes and standard errors for the difference between two standardized mean differences

I have two related questions, both of which are related to a meta-analysis I am performing where where the primary outcomes are expressed in terms of the standardized mean difference. My studies have ...
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75 views

Calculating Hedge's g and its variance from t-statistic

I believe there is a way to calculate Hedge's g and its variance from a t-statistic. I have found the formulas to calculate Hedge's g from one-sample t, and from independent groups t. one sample: ...
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38 views

Obtaining Cohen's d from z-test statistic

After an ANOVA, I run post-hoc tests with the glht function in the multcomp package. glht ...
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3answers
120 views

Understanding $\chi^{2}$ and Cramér's $V$ results

I have two groups of buyers, A and B, and I want to test whether the difference between the percentage of them who would buy a ...
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53 views

Effect sizes from regression analysis and factor loadings

To do a meta analysis, I try to calculate effect sizes. In an article by Shah and Ward, the authors do a regression analysis after combining various factors by a CPA to four factors. The factor ...
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43 views

power analysis when mean and standard deviation are given

I have been asked to perform a sample adequacy test (i.e., I suppose, to verify what is the minimum difference that can be quantified between two grous) where a new sample (of which mu, sigma and ...