# 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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### Is the oft-quoted formula for computing Cohen's d from gain scores correct?

The formula at the end of this quote is given in many places with no citation or derivation. I can't see how the formula can be right, because it isn't dimensionally consistent. The two standard ...
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### Effect Size Calculation from 2-way ANOVA results: Meta-analysis

I am currently extracting data for a meta-analysis on continuous outcomes. I am extracting means and standard deviations for two separate groups (patients and controls) and will later calculate ...
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### Correlation index (r) in matched pair meta-analysis

CONTEXT: We are to perform a meta-analysis of the difference between a and b. In all the collected studies, a and b are the mean times to failure in seconds of two different tasks performed by the ...
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### Confused about the p-value and Cohen's d

I have the following code that computes both the p-value and cohen's distance. ...
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### Calculating effect size

We have conducted a systematic review to investigate the effectiveness of a treatment for a psychological disorder. We aim to report effect sizes and p values of the reviewed studies but one study has ...
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### Cohen's d effect size of a medication

Studies use Cohen's d effect size to convey the effectiveness of an intervention. As a general rule in psychology, an effect size of 0.2 is considered small, 0.5 is medium, and 0.8 is large. Suppose ...
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### How to convert odds ratio to cohens d [duplicate]

I want to calculate the cohens d from adjustad OR, but I think I'm doing something wrong. If aOR = 1.79, N = 600, N_case = 298, N_control = 302, then is the cohen's d 0,139 or 0,321? What formula did ...
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### What is the best statistical test to compare the survey Response rate for a control and treatment group?

We run a survey and want to run a controlled test on a sample of the data. The measure we are trying to improve is response rate. Our research question is: “does sending out more invites to ...
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### Cohen's d or Cohen's d-like effect size estimate for regression slope?

Can Cohen's d be calculated for the linear regression coefficient associated with a continuous predictor? If so, what is the formula? I found one question asking this already, with an answer ...
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### Effect size for marginal means of a model with an interaction term

I'm wondering what is the correct way to calculate the eff_size() of a lmer model with an interaction term. I'm following this ...
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### Measuring treatment effect when only half the the treatment group appear affected

I have data for a set of customers divided into treatment and control, where the objective is to check the impact of treatment on customer’s bank balance. To this purpose, I computed the percentage ...
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### Validity of R pwr package for extremely small sample sizes (<10)

Edit: this question is not: about programming About post-hoc power analysis (at least not with the intent to use sample statistics in post-hoc analysis - I have pretty good population estimates and I ...
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### How can I normalize Hedges' g from two extreme conditions around the control condition?

The variables I am discussing below are not the ones I am actually using but I think that they should give a better sense of what I am trying achieve. I am performing a meta-analysis of some chosen ...
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### Effect size + variance calculation single group pretest posttest - different sample size pretest-posttest

I include single group pretest-posttest study designs in my meta-analysis. I calculate the effect size as follows: difference between posttest mean and pretest mean divided by the standard deviation ...
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### which SD for Cohens D in psychotherapy pre-post study?

I'm reading a study where two groups receive two different psychotherapeutical treatments. The authors calculated Cohens D: 'In addition, we report estimates for Cohen’s d effect sizes as the adjusted ...
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### Help understanding Cohen's D for pairwise comparisons in lme

I've been asked by a reviewer to provide effect sizes for pairwise, planned comparisons. In the experimental design, I have one fixed factor with three conditions (Consistency). Passage & Subject ...
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### Power Analysis for 8x8 factorial within-subjects design (required number of participants/samples)

for an experiment, I was asked to provide a minimum required number of participants using an a-priori power analysis. Thing is, I'm now really confused on how this is possible or even if it makes ...
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### How does G*Power calculate sensitivity in z-test for two independent proportions

I am trying to recreate sensitivity calculation in Python by applying the same methodology as used in G*Power z-tests > Proportions: Difference Between Two Independent Proportions > Sensitivity: ...
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### How to calculate mean difference for effect size calculation?

For a two-sample effect size calculation on paired data (or a one-sample test on differences), does it make sense for an effect size to be negative for a hypothetical % increase of a mean? I’m doing a ...
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### lmer 0-intercept model with binary predictor: Get Cohen's d for difference from zero for both groups

I have a binary predictor group = c("negative", "positive") and this model syntax: ...
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### Computing effect size (d) for lmer() in R

I have selected to compute the Cohen's d effect size for the fixed effects of my linear mixed model. However, it's a little unclear why I'm getting the results I am. First, I am using the method ...
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### Can I compute Cohen d if the data is both non normal and normal [duplicate]

I am working with the data where some samples follow normal distribution while some do not. How to compute the cohen's d if the data is not normal? As some of data is normal and some is not which ...
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### Can I create effect sizes from published reports without access to the data? Thinking about standardizing unstandardized coefficients?

I'm reviewing and synthesizing 48 published articles on the same topic (association between x and y). Instead of describing findings based on statistical significance and power, I'd like to be able to ...
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### calculate effect size from regression table

I am working on power analysis for a project. I want to benchmark effect size from another study. How can I find the effect size (Cohen's d) just by looking at the regression table below? For instance,...
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### How to transform GEE coefficients to Cohen's d (standardized mean difference) for meta-analysis

I am conducting a meta analysis and am looking into how to convert coefficients (with SEs) from a GEE linear estimation into a standardized mean difference, Cohen's d. Does anyone have any hints on ...
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### Is it OK calculating and compare the differences between standardized (z-log) means of different subsets of a dataset?

I have a large dataset of different species-level traits like leaf length, lifespan, height, etc that I am combining with a time-series occurrence dataset to see changes in mean trait values over time....
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I am comparing two sets of samples that are of different sizes (n) and are from two different populations. Both sets have undergone a similar intervention at different time periods (one from August to ...
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### Why is it important to correct for correlated (dependent) measures when reporting Cohen's d?

I am calculating within-group effect sizes from pre-test to post-test. Cohen's dav reports this effect size as a proportion of the average standard deviation (Lakens, 2013): Meanwhile, Cohen's drm ...
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### Effect sizes for GLMs

I'm just checking that I understand things correctly. If one wants Cohen's d-style effect sizes, and you have estimates from a GLM -- say a logit model -- there is no such thing--right? Because there ...
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### Meta-analysis effect size computation

I've been working on a meta-analysis off and on for a while. I am at the analysis stage. Meaning that all relevant effect sizes have been computed. However, I need help understanding what to do when a ...
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### Meta-analysis for studies with both baseline and follow-up measurements in both control and experimental groups

I am new to meta-analysis. I did a quick search, and I think I can wrap my mind around generating cohen's d and its variance when there is only a single distribution for each of the control group (C) ...
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### Calculating Cohen's d

I have two groups (experimental and control) and a measure (an estimate of confidence) measured at baseline and at post-intervention. I have ran a multiple regression and found that the intervention ...
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### What's the appropriate effect size estimate (and power analysis) for post-hoc regression?

I've seen some similar (ex ex2) questions, but hopefully this is not a duplicate. As it is mentioned in one of them, I'm using eemmeans to do pairwise comparisons ...
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### Can I compare a Cohen's d to a log-response ratio in a meta-analysis?

I'm conducting a meta-analysis and I'm wondering if I can make direct comparisons between different types of effect sizes? For example, can I compare a Cohen's d calculated from one study to a log-...
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### Calculating Cohen's d from standardized or unstandardized regression coefficients (GLM/GLMM) for meta-analysis

I am currently conducting a meta-analysis about the effect of blood parasites on different fitness parameters of song birds. Since I have a rather large number of parameters that I want to incorporate,...
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### How to Simulate T-Values for Two Different Samples

Motivating Question I had a discussion with somebody recently, who said that a 10 participant sample with a t-value of 2.1 is more impressive than the same t-value for a 100 participant sample. The ...
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### Inter-rater reliability (complex survey )

Help calculating Inter-rater reliability in a complex online survey (free text). The questions are free text. We have now coded the potential answers. Examples: 1.) Hobbies (Time in nature, mind-body ...
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### When calculating a standardized change score, what do you divide by and why?

I understand that, in most cases, one calculates a standardized change between two scores as (Lakens 2013) i.e., the mean of the change scores is divided by the standard deviation of the change ...
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### Cohen's D on transformed data for effect sizes

I have given data for users which is right skewed with a long tail, meaning high gmv is driven by few users. Now I have 2 cohorts of users for whom I want to compare gmv distribution. My first ...
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### Underlying assumption for calculating cohens D

Is there any underlying assumption when we can reliably use Cohen's D? Do we assume our samples should be Gaussian? I know that Cohen's D is heavily biased by outliers and sample size. But is there ...
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### Comparing Cohen's D and Arcsine Transformation in Meta-analysis

I'm conducting a meta-analysis that consists of 15 studies and ~40 construct effect sizes. Most of the constructs and studies use continuous variables and were straightforward in finding standardized ...
1 vote
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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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### 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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