Questions tagged [cohens-d]

Cohen's d is a generalized effect size measure. It is the difference between two group means scaled by the combined standard deviation. Cohen's d is used frequently in Jacob Cohen's text on power analysis, mostly to simplify the presentation of tables.

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Converting Cohen's $d$ to Pearson's $r$ $\ne$ calculated Pearson's $r$

I was calculating effect sizes for an analysis and noticed by chance that Pearson's $r$ calculated from Cohen's $d$ with a conversion formula is not the same as when I calculate the correlation given ...
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Meta analysis for a number of identical studies (with access to raw data)

I have access to about ten almost identical studies from ten different locations. They have been done different years, but with the same methodology. Each site was analysed and reported separately ...
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Meta-analysis with rma() in metafor

I am working on a meta-analysis that has two moderator variables. Below is the code that I've figured out, but I'm not sure how to get the forest plot to show the overall model estimate. It's ...
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One-sampled t-Test: large Cohen's d and large p value (is there a statisctical error?)

The p-value from a t-test I have run is unexpectedly large, considering Cohen's d. I calculated the one-sample t-test in RStudio for the following hypothesis: H2: For athletes who have already reached ...
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Effect size and statistical significance correspondence

While I understand that it is possible to have a small effect size with statistical significance and a large effect size without statistical significance, is it ever possible to find this across two ...
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Hypothesis testing Cohen's D -> actual difference in means (proportions)?

I'm trying to execute power analysis regarding proportions (successes of trials.) Using Python's stats models package I can specify a number of trials, an alpha and a beta and the MDE returned will be ...
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Calculating global and local effects in a multiple regression using Cohen's d

I am calculating the effect size Cohen's d using linear regression. I am looking at the effect of disease on memory, and have also added age, education and sex as confounds to the regression. Cohen's ...
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Transformation eta sqaured into cohens d or r

Is there a possibility to convert eta squared to Cohen's d or r? I uded this page (especially calculator 14) to transform different effect sizes into one: https://www.psychometrica.de/effektstaerke....
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Cohen-d issues with pingouin ttest function for paired samples

I have two lists of time values, 'times0' and 'times1'. The data are paired (first value in times0 is paired with first value in times1, second value idem etc etc). I want the cohen-d of the t-test ...
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common effect sizes in psychological research and calculation/ transformation

I am working on an empirical literature analysis. For that I have to code some variables in a specific manner (analysis includes 150 published studies in the field of behavior Neuroscience, ...
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How do we call the distribution of a ratio consisting of a constant divided by a truncated normal random variable?

I have been thinking for a while about the following problem of Cohen's d effect size measure $d={\frac {\mu _{1}-\mu _{2}}{\sigma}}$ in random-effects meta-analyses for which I cannot find a more ...
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Can I calculate Cohen's d (effect size) by hand if I have two means with their SD in a within subjects design?

I have several within-subjects studies that assess more or less the same intervention, but measure the outcome with different outcome measures. Most of my studies display the outcome in mean ± SD, ...
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Equivalence test to compute no-differences between variables?

I need to state that there is no difference between the outcomes of the two tests (method 1 = fast and simple, method 2 = slow and hard to reproduce). I thought that a non-significant t-test would be ...
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Converting unstandardised regression coefficients to Cohen's d for meta-analysis

I am conducting a meta-analysis of Cohen's d and some raw effect sizes are unstandardised regression coefficients. Of these unstandardised regression coefficients: Some are based on a binary ...
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Target population for power analysis of ML model A/B test

We are working on an ML model that predicts a numeric result (call it $\hat{x}$). Eventually, we will perform an A/B test, where the metric is a function that takes $\hat{x}$ as an input (call it $f(\...
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Cohen's d for Longitudinal Data - Between Group Comparison

I am trying to calculate Cohen's d for longitudinal data. Specifically, I want to calculate the effect size for the post-time point between two groups (treatment vs. control). I have built a ...
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Why, in simple terms, is Cohen's D not affected by sample size but a T-Test is?

Why, in simple terms, is Cohen's D not affected by sample size but a T-Test is? I don't really understand and tbh am struggling to tell the difference between the two at all.
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Sample sizes for two independent samples w dichotomous outcomes

I have two groups of very unevenly distributed data, one group has 95% more observations than the other group. My outcome variable is a binary variable. I know how to calculate the effect size, but I'...
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2 outputs when calculating Cohen's d

I've just tried to calculate Cohen's d in R with the following formula: ...
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Convert correlation r to Cohen's d (unequal groups of known size)

I am doing a meta-analysis. I would like to estimate Cohen's d for various studies. The correlation is made up of (a) a binary variable and (b) a numeric variable. I also know (a) the mean for the ...
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How to compare different effect sizes (d vs. r)?

My question is whether I can compare two different effect sizes (Cohen's d and r). I have tested the differences between two paired groups regarding different variables. They are paired because they ...
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Why is the cohen's d effect-size from this study so different from the value I've computed manually?

In this study [1], they estimate an overall cohen's d effect-size of .70; however, when I try to compute the cohen's d using their means/stds, I get a much smaller effect-size of .47. Am I doing ...
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Two methods of converting Cohen's d to CL (common language effect size / Probability of Superiority) yield different results?

The common language effect size (CLES) of McGraw & Wong, 1992, also known as the probability of superiority, can be conceptualized as the probability that a person picked at random from the ...
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How can I take into account the different sample sizes of the two groups that I am comparing with a t-test or analysis of variance?

I am computing a p-value using the aov function in R in order to detect if the means of two groups are significantly different. However, these two groups that I am ...
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Converting Hazard Rate Ratio and Relative Risk to standardized effect size (eg Cohen's d)

We are 2 psychology students writing a systematic review. We need to convert the effect sizes from the different studies to Cohen's d (or another standardized effect size). Can anyone help converting ...
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Cohen's d and standard deviation from t-test in r

I am looking for how to determine the cohen's d for my t-test so I can make a post-hoc power analysis take the following: the data: ...
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Convert percentile change to Cohen's d

tl;dr: How do I convert from percentile change to Cohen's d for the whole distribution? A common measure of effect size is Cohen's d: the mean difference between an experiment and control group ...
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Comparing coefficient across groups in 3 way linear mixed model

I wonder how to compare coefficients across group in linear mixed model. Dependent variable (DV, continuous variable) is changed by time variable (T, continuous, fixed effect). And hypothesis is that ...
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Confidence intervals of Cohen's d in controlled pre-post trials

The design with two sessions and two groups (treatment and control) is quite common. How can I calculate the confidence intervals for Cohen's d for that design? It is said that in this design we ...
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How to compute Cohen's d when provided percent difference and standard deviation?

I am trying to compute Cohen's d from a published paper. M1 and M2 were provided as percent differences (the average difference in scores from t1 to t2 for an experimental group and then a control ...
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Rubin's rule, applied to absolute effect size or relative effect size (Cohen's d)?

Cohen's d is a way to describe the effect size relative to the standard deviation of the data. For instance in the case of the difference between the means of two populations $$\begin{array}{} \text{...
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What is the formula for the standard error of Cohen's d

I found different answers to the question how to calculate the standard error (SE) of Cohen's d. First formula is (see here, here or here): $$ SE_d = \sqrt{\frac{n_1 + n_2}{n_1 n_2} + \frac{d^2}{2(n_1+...
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How to interpret a large Cohen's d when p-value is non-significant and CI's are close to 0

I have a sample size of 23, with 11 and 12 participants in each group. I conducted t-tests for several continuous dependent variables. All of them are non-significant, but some of them have quite high ...
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How to convert a negative binomial regression coefficient to an alternative effect size?

I am conducting a meta-analysis and the effect sizes are mostly Cohen's d or log odds ratios. However, a few of the effect sizes are regression coefficients obtained from negative binomial regressions....
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Is the squared Cohen's $f$ the same as Cohen's $f^2$?

Question Is the squared version of Cohen's $f$ the same as Cohen's $f^2$? Or do they only share the same letter by coincidence? Explanation At first, I wondered if one can simply square Cohen's $f$ to ...
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How to calculate Cohen's d between multilevel model predictions at two points in the domain?

I would like to get a Cohen's d between model predictions at different points in the domain of a mixed effects model. I have model predictions and I have bootstrapped standard errors. I mention the ...
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Cohen's $d$ after linear regression

Assume the model: $$Y = \beta_0 + \beta_1x_1 + \beta_2x_2 + \varepsilon$$ Where $x_1$ is a continuous variable of no interest and $x_2$ is a group variable (0/1). I would like to estimate the effect ...
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standardized mean difference including between and within subject designs

I am in the process of drafting a meta-analysis for a research project. The document makes use of a forest plot (random-effects model) that depicts the standardized mean difference of each study along ...
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Finding effect size from a research paper

I am writing a review paper under a prof this summer, and I'm desperate to demonstrate that I am competent, despite being as inexperienced and unqualified as possible. I am working on a compiling the ...
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Statistical comparison for large sample sizes (n>1000)

I am comparing the drug exposures across two different groups, consisting of 1000 simulated drug exposures per group. Drug exposures are continuous variables following a normal distribution. I want to ...
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Calculating variance of one-sample cohen's d effect size

I'm trying to perform a meta-analysis where my effects are mainly one-sample t-test against chance level. I've easily found the one-sample cohen's d formula but I'm not able to find the variance ...
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Difference between Cohen's d and beta coefficient in a standardized regression model with dummy coded predictor variable

I have been wondering about this for a while now and I just could not find an answer to it, so I'd be glad if someone here could help me out! If I have a simple regression model with a standardized ...
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How do you calculate cohen's L so that you can plug it into a power calculation for multiple linear regression?

I am reviewing a book called Statistical Methods for Healthcare Research so I can learn how to do a power calculation for my sample size for multiple linear regression. This book says that cohen ...
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What is the intuition behind Cohen's d?

Can anyone please help me in understanding what does the result of Cohen's d gives us? Like how do we interpret the results and what does the positive and negative sign mean?
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Cohens d effect size calculations across 3 groups

Is it possible to calculate a single Cohens d effect size, across 3 groups? I have successfully used Cohens d to calculate the effect sizes between state 1 and 2 (as simple example given below) for ...
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Compare/Interpret t-statistics

I've a table as the following that contains the results of one sample t-test on four independent collections for the null hypothesis that the mean is 0: ...
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Wrong sign for cohen.d {psych} in R?

I'm trying to calculate Cohen's d with cohen.d from the {psych} package in R. So this is the descriptives output (means of variables for groups): ...
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How should I calculate sample size when Cohen's $d$ effect size is $> 5.6$?

I am working in R. I am doing some simulations of sample sizes by drawing random samples from two normal distributions. I am calculating Cohen's $d$ effect size with: ...
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Two different versions of Cohen's D? Which one to use?

I am trying to measure the effect size of some variables between two different groups. I've taken some python code from a few tutorials, but they seem to be calculating it in different ways. I ...
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Compute standardized mean difference and its standard error from regression-adjusted mean and 95% CI for 2 groups

I am working on a meta-analysis (using aggregated data), where the outcome is a continuous variable. One study reported post-treatment outcome values as regression-adjusted mean and 95% CI in each of ...
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