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

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1answer
45 views

How to convert from Mann-Whitney U to Z (or other effect size)?

I'm looking at multiple studies. I do not have the original data. One study I'm looking at provides means, standard deviations, and Mann-Whitney $U$ values (with $p$). (How) can I convert from ...
1
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2answers
31 views

When are odds ratios worse/better than risk ratios as measures of the effect size of associations between categorical variables?

Wikipedia gives some information on this. However, I seek more detailed information on when odds ratios/risk ratios are better, and why one is better than the other in certain circumstances.
1
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1answer
94 views

Does one lose information or precision when calculating effect sizes from statistical values rather than from the raw data?

Let's say that I want to compute the effect size of a certain intervention, for which I have both the raw data and some statistical value that can be transformed to an effect size. For example, if one ...
6
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2answers
80 views

In a meta-analysis, how should one handle non-significant studies containing no raw data?

Let's say that I'm conducting a meta-analysis, looking at the performance of group A and group B with respect to a certain construct. Now, some of the studies that I'll come across will report that no ...
2
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1answer
55 views

direction of effect size

Should my effect size be positive or negative when the control group gains more weight than the experimental group (when it is hypothesised that the experimental group would lose more weight i.e., the ...
0
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0answers
28 views

one-way MANOVA effect size interpretation

I'm having problem understanding effect sizes in one-way MANOVA model. In my case, I'm having a 13 variables which I used for clustering and then the produced ...
6
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2answers
198 views

Bayesian analysis of contingency tables: How to describe effect size

I'm working through the examples in Kruschke's Doing Bayesian Data Analysis, specifically the Poisson exponential ANOVA in ch. 22, which he presents as an alternative to frequentist chi-square tests ...
0
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0answers
32 views

Variable magnitudes and principal component analysis

I am completing some PCA on various sets of data, some with 30 time-series variables, some with about 100 (meaning matrices with between 30 and 100 columns). I know that the covariance matrix is ...
1
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1answer
23 views

(Inverse) proportionality between significance and effect size, for a fixed sample size?

This is a question to hopefully untangle the sometimes confounded notions of statistical significance and effect size. As far as I understand, sample size intermediates the relationship between them, ...
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0answers
30 views

Does Greenhouse-Geisser correction influence the effect size estimation, the statistical significance treshold, or both of them?

I discussed recently with one of my colleagues about the Greenhouse-Geisser correction for non-sphericity. I told him first that this correction is very conservative and that it would be more ...
3
votes
1answer
75 views

What do you do after testing if two non-normal distributions differ?

This is a follow up question to "How do I test if two non-normal distributions differ? I have 13 distributions, . According to the previous question, I should do the following. Kruskal-Wallis test ...
1
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1answer
63 views

Strength of association test with binary variables

I have a dataset with different purchases for two different items from the same users. So the users purchased the two items at different points in time. I also have 3 different variables: ...
0
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0answers
19 views

Very different group sizes - categorical variable

I would like to test for a difference between 3 groups for a binomial variable. There are around 400 in one group, 900 in the other group and 100,000 in the third group. I am wondering if this huge ...
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0answers
39 views

Absolute effect size and relative effect size in HLM

I am having trouble figuring out what the regression equations for HLM models are with absolute effect size and relative effect size provided in a table. E.g., the outcome variable is reading test ...
11
votes
1answer
429 views

Is a priori power analysis essentially useless?

I attended a meeting of the Society for Personality and Social Psychology last week where I saw a talk by Uri Simonsohn with the premise that using an a priori power analysis to determine sample size ...
3
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0answers
78 views

Looking for beginner resources with effect sizes

First post here; first I would like to say that I have no background in stats whatsoever and not so much in math either (enriched high school math, and that's it). I started an MA and we have to do a ...
1
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2answers
41 views

Does filtering of data by effect size violate some assumption of P value adjustment methods?

I have pre- and post-treatment continuous data for a large number of variables that I am analyzing for treatment effect. Normally I would obtain the P values and then adjust them for multiple testing ...
5
votes
2answers
92 views

Conflict in confidence intervals for mean difference and confidence interval for Cohen'd effect size

I run an experiment to compare the performance of two algorithms. The design of my experiment is paired comparisons. I'm reporting my results in this way: There were no outliers in mean ...
3
votes
2answers
85 views

What does it mean that the true effect size is not known?

I just read this statement: In neuroscience the true effect size is not known What does this mean? In contrast, what does it mean that where the true effect size is known?
3
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0answers
36 views

Cohen's d, but using mean absolute deviation

A common measure of effect size used in the social sciences is to look at the standardized difference in means between two conditions (Cohen's d). That is, take the difference in means between two ...
1
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1answer
113 views

How to work out Effect Size for a MANOVA using G*Power

I'm using G*Power to work out how many participants I need. I'll be using a MANOVA, I have two independent variables (Male and Female) and they will be answering 13 different questionnaires so 13 ...
0
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0answers
65 views

Effect size in plotLMER.fnc

I'm working with linear mixed models. I used plotlmer.func, in the package lmerConvenienceFunctions to build a graphical ...
1
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1answer
70 views

Prevalence conversion to effect size in meta-analysis

I'm used to thinking about meta-analyses in terms of evaluating the impact of an IV on an outcome of interest (ex: relationship between a teacher's level of self-confidence and student outcomes), and ...
4
votes
2answers
62 views

How can I calculate the effect of my equipment on my sport's performance?

I'm doing a stationary sport like golf, so the details matter. I'm recording each of my scores with detailed information about the equipment I'm using, and the weather conditions. So 1 score has 2-3 ...
0
votes
1answer
82 views

Effect size in R (check significance level for bigger sample)

In my current analysis, I have not found statistical significance to some of my conditions. So I was wondering how to predict or calculate the effect size with more subjects and items. I have 20 ...
2
votes
2answers
177 views

eta-squared by hand

This code outputs the eta-squared from an ANOVA: ...
1
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1answer
137 views

How to calculate cumulative standards errors from several ones?

I want to estimate the cumulative effects of air pollution on mortality using GLM or Gam methods. With the following R code I was able to estimate the cumulative effect of PM10 on mortality which is ...
0
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0answers
55 views

Power Analysis and effect size

Appology if it is rather long. But i'm confused! What assumptions do i need in order to answer this question? With having two segments in the population that you wish to compare with respect to their ...
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0answers
71 views

Calculating effect size variance from adjusted means (or least squared means)

I have a question related to this post regarding the calculation of the variance of an effect size. In my specific case, I would like to calculate the effect size and its variance from adjusted means ...
0
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0answers
111 views

Cohen d for 2x2 interaction

There is a nice answer to this question, but it assumes that you have the ANOVA table available. My problem is different. Say I'm reading a paper describing a male vs female, disease vs control ...
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0answers
127 views

Correct calculation of effect size after Friedman test in a skewed population

I have some data that compares behaviour in four conditions (repeated measures)(I have several different behavioural variables and each behaviour gets analysed separately, and the behaviours are ...
1
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1answer
98 views

Reporting operative effect in paired t test

I just want to make sure I have something clear in my head. When I calculate the effect size for a paired samples t-test after obtaining a significant result, I simply take the mean of the differences ...
0
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0answers
59 views

eta-squared in GLM

If I am right, you can calculate eta-squared in an ANOVA by: SS (covariate of interest) divided by SS (total) I was wondering if the calculation and interpretation is the same in a General Linear ...
0
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0answers
79 views

Sample size and correct choice of test in g*power

I am new to g*power and have a question about which test I have to choose and how to interpret the given sample size. I have 2 measurements (pre / post), one control-group and one intervention-group. ...
0
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0answers
121 views

Meta-analysis comparing difference between pre vs post treatment group vs pre vs post control/placebo group

I am hoping to obtain ES of 20 studies, each having pre vs post treatment compared to pre vs post placebo (i.e., is there a way to obtain ES through difference in means between the two groups and ...
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2answers
196 views

Is Cohen's $d$ a better measure of effect-size than a simple mean difference for a meta-analysis?

Cohen's $d$ measures the difference between the mean for the experimental group and the control group divided by standard deviation. The Cohen's $d$ statistic produces something that does not add to ...
0
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0answers
70 views

Calculating Effect Size in R

I've been trying to learn about effect size in relation to linear regression and am wondering how to implement it in R. Sure, I have p-values and they indicate how "predictive" the explanatory ...
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0answers
60 views

Reducing sample size to change from a paired to unpaired design

I have two groups of data, one consisting of 9 subjects and another consisting of 5 subjects. In the 9 subjects group, 5 of those could be paired with the 5 subjects from the other group. I could run ...
3
votes
2answers
269 views

Critical effect sizes and power for paired t test

Is there some sort of easy way to calculate the required sample size for a paired t-test with an effect size of 2 standard deviations? In my line of work, we often use an effect size of 2SD from the ...
2
votes
2answers
201 views

Calculate effect size using raw or log transformed data?

I'm basically wondering whether log transformed data or raw values should be used to calculate: effect sizes change scores the standard deviation (SD) for the precondition I know that SD of ...
2
votes
1answer
149 views

How to estimate a standardized mean difference from two samples' quartiles?

I'd appreciate ideas about how to estimate the standardized mean difference (SMD) for two independent samples from each sample's size and middle three quartiles (i.e., median and 25th and 75th ...
3
votes
1answer
86 views

Cramér's $V$ on Rao-Scott adjusted Pearson $\chi^2$

I have survey data with design weights for stratified sampling. My ultimate goal is to estimate Cramér's $V$ for contingency tables, a Pearson $\chi^2$ based measure. To account for the weights, I am ...
3
votes
1answer
139 views

Measures of effect size for chi-squared tests

What are the different measures of effect size used for chi-squared tests / binomial data? I'm already at least somewhat familiar with the phi coefficient and odds ratio. I've heard of Cramer's V and ...
3
votes
1answer
760 views

Converting odds ratios to Cohen's d for meta analysis

I'm conducting a meta-analysis largely on mean differences data, however I have several articles that report only an odds ratio, N, p value, and confidence interval, and I need to convert this ...
2
votes
0answers
193 views

Understanding the one-way ANOVA effect size in scipy

I'm calculating F- and p-values using the scipy.stats.f_oneway ANOVA function and I'm having trouble interpreting the effect size f-values. I'm getting numbers well above 100 in some cases, whereas ...
6
votes
2answers
108 views

What is the $\mu^2$ squared effect size?

I was recently looking at a paper in the journal Psychological Science and came across this: F(1, 71) = 4.5, p = .037, $\mu^2$ = .06 F(1, 71) = 0.08, p = .78, $\mu^2$ = .001 I was wondering what ...
4
votes
2answers
573 views

What's the difference between Hedges' g and Cohen's d? [duplicate]

I have been reading http://www.polyu.edu.hk/mm/effectsizefaqs/effect_size_equations2.html and the only difference I can find between the two is that they have ever so slightly different pooled ...
0
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0answers
17 views

Controlling for medication effects in case-control comparison

Say as an example problem you are comparing BMI between two groups, one group is healthy (CTL) and the other has been diagnosed with bipolar disorder (BPD). Some of the BPD patients are taking a ...
0
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1answer
36 views

Is it possible to generate means and standard deviations for two groups based on a Cohen's d?

Is it possible to generate means and standard deviation for two groups from a Cohen's d effect size? Even if the means and standard deviations are trivial/meaningless values, I would like to keep the ...
1
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1answer
112 views

Is effect size (Cohen's d) scale data or just ordinal?

I am aware that you must be careful about when you can compare effect sizes. But let's assume that I have two effect sizes from two similar studies: similar groups, same intervention, same ...