# Tagged Questions

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

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### Variance explained in multilevel model - why based on covariance parameters & not information criteria (-2LL)?

In logistic regression, using Hosmer Lemeshow's approach, the effect size or variance explained is the amount of reduction in -2LL of the developed model (which equals the chi square statistic of the ...
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### Pearson correlation is not significant although effect is .30 What could be the reason?

I have a correlation between two variables of 0.30, hence a medium effect. but it is not statistically significant and I want to report the reasons for that. looking at the test statistic I see that ...
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### What test to asses the complication a treatment has with a small sample size(80) and only 5-10% complication rate?

I am assessing the benefit of using a therapeutic intervention in a population of 80 people split evenly into two groups. The benefit is to decrease a certain complication which only has a incidence ...
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### Pretest-posttest plus control design

I am evaluating the effect of an intervention (treatment: a lecture) on the ability to spot behavioral clues of emotions using visual stimuli using pretest-posttest plus control group experimental ...
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### Difference between Cohen's d and Hedges' g for effect size metrics

For an effect size analysis, I am noticing that there are differences between Cohen's d, Hedges's g and Hedges' g*. Are these three metrics normally very similar? What would be a case where they ...
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### Can a sample be too large for ANOVA or a t-test?

I have close to a million data sets and whenever I run mean comparison test, either ANOVA or a t-test, I get a significance level of less than .0001 on SPSS. I'm concerned that my sample is so large ...
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### Effect size with unequal sample sizes

I would like to know if anyone can help me calculate the effect size for a chi square (two sample proportion z-test) for different sample sizes. I am using $\phi$ when sample sizes are equal, but ...
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### partial eta squared

Would it please be possible to help me with a statistics query. I have asked for the partial eta squared on the output of a one-way within subjects ANOVA from SPSS and it has given me the value .137. ...
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### How do I interpret a significant interaction effect that has a low effect size?

I am comparing measures of a DV x with two group factors (2-way ANOVA) - y (with 2 levels) and k (with 3 levels). Both present significant main effects (p<.001) and high partial eta squared (above ...
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### Confidence interval of the ratio of two means for very small sample sizes

I have an experiment with 3 tanks for, both, treatment and control. I have used a natural logarithm of response ratio (LnRR) with 95% confidence intervals to examine the effect size of the treatment ...
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### What is the effect size for the interaction of a 2X2X2 contingency table?

I am computing the interaction in several 2X2X2 tables (i.e. in each case, I have eight frequencies), see for an example this file. I have two predictors (low vs high 'threat' and low vs high ...
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### Literature to support effect size over significance

In a large sample (N = 3,265,506 for my study) tests are always significant. Is there an article in the literature I can cite to justify using effect size instead of significance testing?
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### Multiple Imputation - calculating effect size and reporting results

I'm analyzing the change of various psychometric features that are supposed to change during treatment and their relation to some other features (I don't think I have to go much into detail here). My ...
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### Effect size in contrast analysis

I'm running 2-way repeated measures ANOVA (3 and 5 levels) with planned contrasts afterwards. I'm interested in comparing 1)levels of the first factor among themselves (e.g. A1B with A2B, A2B with ...
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### The use of effect size

I was able to calculate the sample size using two different effect sizes 0.3 and 0.5 and each gave me different sample sizes. 0.3 gave me 82 and 0.5 gave me 26. I have 45 students in that gradelevel. ...
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### Comparing Algorithms using AUC, Effect Size, or Box-plot?

I want to compare the performance of two algorithms (one semi-supervised and the other one is an unsupervised algorithm like SVM or Naive Bayes) based on Hedges' effect size calculation). For this ...
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### How to assess effect of intervention in one state versus another using annual death rate data?

I am a beginner in statistics. I have these unpublished data (cases and deaths) of a disease for 7 years (2004-2010) from 2 neighbouring states. The study was started in 2004. State 1 and State 2 ...
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### Standard deviation for adjusted effect size estimates

I am trying to calculate the effect size for a trait adjusted for my set of nuisance variables. My models looks like this: Trait ~ Dx + Age + Sex Where "Trait" ...
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### Effect sizes from LMM

My question is, how to get effect sizes for a linear mixed model? I am using the following model in SPSS: ...
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### Whether to report confidence intervals of effect sizes such as $r$ and $\eta^2$?

I have calculated the bivariate linear correlation coefficient between $x$ and $y$ and it is $r= 0.45$; $p<001$. I know $r$ is a measure of effect size. Should I also be reporting the ...
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### Effect size and signal detection

Are d prime (d') in signal detection theory and Cohen's d (mainly reported in the context of the general linear model) measures for the same thing (i.e., the difference of the means in SD-units), and ...
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### Does pooled variance correct for/protect from unequal variance when calculating effect size?

This may be a lame question, but I got stuck and can't get my head around it. I am running a gene expression analysis, comparing ~10000 genes between two groups, n=6 samples per group. My pipeline ...
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### What is the pooled standard deviation of paired samples?

I am trying to do a priori sample size calculation based on published results. However, I am unable to obtain a reasonable estimate of the published effect size (which is not reported) as I am unable ...
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### How to compute effect size for different measures of association?

My colleagues and I are looking for guidance on how we might compute a common effect size (ES) from the following measures of association: Pearson's r Spearman's rho Kappa ICC / intraclass ...
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### Can the influence of a different factor on a known effect be analyzed directly?

If I am trying to analyse wether a known effect is inhibited by another factor, is it a fallacy to analyse the influence of the factor on the effect size directly? I.e. can I just use a statistical ...
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### How to assess whether two treatments are significantly different using Cohen's d (effect size)?

Cohen's d is a measure of effect size calculated as: $d = (x_1-x_2) / \sigma_{\text{pooled}}$ where $x_1$ is the mean of one group, $x_2$ is the mean of a second group, and $\sigma_{\text{pooled}}$ ...
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### Effect size and statistical significance

Using Cohen's d, I am getting small amd medium effect sizes for results that are statistically non-significant (p>.05). Does this make sense?
### $\eta^2$ and paired t-tests
When doing a paired t-test, is it appropriate to use the paired t value to calculate $\eta^2$? I ask because it is not appropriate to calculate Cohen's d based on the paired t value. Thanks.