# 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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### Independent t-test with multiple imputation including pooled effect size (R, mice)

I just started using multiple imputation in R using the mice package. I want to conduct an independent t-test on the imputed data. Here's a minimal working example:...
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### Approximating standardized effect-size measures, Cohen's d from glmer model

I'd like to compute the Cohen's d, of glmer model's fixed effects. These are the steps I'm following: Building a model ...
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### When to use Cohen's d and when t-test?

When do I use Cohen's and when do I t-test? Probably in addition: What is the (conceptual) difference between them? Both tests are meant to study the difference between two distributions. I just ...
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### Converting Cliffs delta to Cohen's d

I need some help converting effect sizes and calculating 95% CI for these effect sizes. I have a pilot study with 17 participants who completed 4 likert scale measures (Variable 1, Variable 2, ...
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### Cohen's d for 'time' and 'groups' from repeated ANOVA

I have computed partial eta squared (np2) from a two way ANOVA with repeated measures using SPSS. However, I'd like to convert np2 into Cohen's d for time and groups or at least understand a cite ...
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### Can the r-scale value (for Bayes Factor) be directly based on Cohen's d?

I want to set an r-scale value for a Bayesian t-test (i.e. to calculate Bayes Factor likelihood ratio) based on previous results (i.e., from a posterior). But I simply cannot find a straightforward ...
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### Reasons for reporting Pearson's r for / alongside standardized mean difference effect size (Cohen's d)

What are the practical use-cases and / or reasons for reporting Pearson's r alongside Cohen's d? This question is a followup to this post where the conversion itself is discussed. Since r calculated ...
1k views

### Converting between correlation and effect size (Cohen's d)

Several sources (here here here) claim that there is a relation between Cohen's d and Pearson's r if the data is paired (bivariate). This strikes me as odd since, for example, evaluating a "before and ...
113 views

### Meta-analysis with response ratio effect size

I am interested in comparing the performance of two different techniques (i.e., Method A vs. Method B) on a continuous outcome of interest. The performance of such techniques is measured through test ...
170 views

### Meta analysis Cliff's delta

Cliff's delta is an effect size typically recommended whenever the normality and homogeneity assumption do not hold---and thus, Cohen's d cannot be used. However, I cannot see any reference ...
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### Are effect sizes on different populations comparable?

Does it make sense to conclude that an effect is (likely) stronger in population A than in population B because the effect size estimated on A is larger than that estimated on B? (The samples are not ...
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### Cohen's d and Sten scores

Can someone explain why Cohen's d of sten score is 2 times of Cohen's d of SD? Thanks. The question is based on the paragraph below: *When looking at differences it is useful to remind ourselves of ...
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### Network meta analysis without standard deviations

I am trying to compute Cohen's in some studies that I gathered in a Systematic Literature Review. Unfortunately, almost none of them report the standard deviation (nor df/t, or something for back-...
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### What is the difference between Cohen's d, ANOVA, and Regression?

It is my understanding that ANOVA, Regression, and Cohen's d each measures the distance between means of two or more groups. If that were the case, then what is the purpose of having different methods ...
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### How to compare two age distributions in a population of people?

I have data on a number of clubs and the ages of their members broken down into categories from 0 to 94 and then a final category of 95+. I have about 10,000 clubs and I need to compare how similar ...
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### Cohen's d calculation when within group variance is zero

We have a single-case experimental design and we calculated Cohen's d for effect size using the mean difference between pre and post, divided by pooled standard deviation. However, for one of the ...
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### How do I calculate an effect size (cohens d) from a % difference between interventions and control

If I am basing results on a previous study which has a difference between intervention groups (5 intervention groups) and 1 control of 10.9%. How do I calculate the effect size (d)? I want to be ...
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### Cohen's d from a linear regression model

Problem: I have a multiple regression model with categorical/binary ($c_i$) and continuous ($x_i$) variables: $v = \alpha + \beta_1 x_1 + \beta_2 x_2 + ... + \gamma_1 c_1 + \gamma_2 c_2 +$ I am ...
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### Converting Cohen's d to a Relative Risk for a model-based economic evaluation

Hello researchers: my question is about the use of forest plot results for an economic model. In a forest plot you could have the following results: 0.34 [0.22, 0.45], which would be the pooled ...
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### Power calculations using pilot effect sizes

Pilot sample sizes can yield inflated effect size estimates. After conducting a pilot I have found the 95% confidence interval on my effect to have a wide range due to the small sample size. How ...
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### Calculating Cohen's d for pre-post/treatment-control design where treatment-control is also a repeated/within factor

I'm conducting a meta-analysis of studies that used pre-post/treatment-control designs. Most of them are mixed designs (pre-post is repeated/within; treatment-control is independent/between) with a ...
106 views

### Calculating/Averaging/Aggregating Effect Size Across Multiple Measurements

What is the standard practice for calculating a total effect size (using Cohen's d) across multiple measurements in one study? Do you calculate the effect size for each measurement and then take the ...
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### Calculate Cohen's d from mixed repeated messures ANOVA

Can someone calculate Cohen's d for me from these data? F(4, 42) = 39.37, p = 0.001, eta squared = 0.48 There were 3 groups measured on 3 times (pre-treatment, ...
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### Deriving an effect size from previous literature for determining a required sample size for a clinical trial

I'm looking to do a pre-posttest RCT comparing difference of means through a t-test, however I'm completely unsure how to calculate a required sample size using power, confidence level, and ...
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### Is it more accurate to convert t-test statistic to pearson's r or means and SDs to cohen's d to pearson's r when extracting data for a meta-analysis?

I am completing a meta analysis and the common metric I am using is pearson's r. For studies that report comparisons of means rather than correlations should I convert the t-test statistic the author ...
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### Using R: Why I always get different Cohen d values?

Hopefully someone can help me as the question drives me completely crazy. I'm using R to calculate Cohen's d with the following code and every time I get different results. What am doing wrong? <...
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### How can Cohen's d < 1.96 ever be statistically significant?

I am having trouble understanding the statistical significance of Cohen's d. My reasoning goes like this: To conclude that experimental group differs from control group significantly (p < 0.05), ...
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### Mini-metanalysis repetead mesures ANOVA 2x2 interaction

I performed two studies on the relation between the stimulus valence (positive/negative) and the action tendencies (approach/avoid) measured with TMS motor evoked potentials technique. For each study ...
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### Cumming's ESCI calculator for within-subjects Cohen's d & 95% CIs

I am calculating Cohen's d and 95% CIs for a within subjects t-test. Cumming's ESCI calculator only estimates the 95% CIs for Cohen's d when df < 200. Is there a theoretical / statistical reason ...
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### Cohen's d / Hedge's g: when to use 'paired' vs 'pooled' method

When calculating Cohen's d or Hedge's g, one can opt to use a paired or pooled method in handling variance. I am working with a small sample size (up to 12 observations in each sample being compared),...
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### Can Cohen's d be used for distributions that are not normal?

Can Cohen's d be used for distributions that are not normal? Or is it used only to compare normal distributions?
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### Using transformed data in Cohen's d effect size calculations

I have used a Log10 transformation on my data to transform some non-parametric data to normally distributed so that I could run a Pearsons correlation. Field (2013) states that only problematic ...
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### Calculating Cohen's D for a contrast

I have run a t-test contrast by dummy coding three groups. Let's call them A, B, and C. The contrast is A and B against C. Now, I want to calculate an effect size for the resulting t-test. I am not ...