# Questions tagged [group-differences]

Group differences broadly refer to statistics which quantify the differences between two or more subpopulations.

436 questions
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### Dependent tests?

I have 3 independent data groups: A, B, C. I performed t-test on each pair of groups: AB, AC and BC. So these three tests (AB, AC, BC) are not independent, are they? Thanks for answer!
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### What statistical tests would you recommend for group difference for my data?

I am trying to find out what statistical tests to run on a set of aggregate data (no individual data) on 3 different groups, variables are summarized below: Group 1 in site 1: Mean value (blood sugar) ...
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### Comparing distributions of unequal sample sizes

Consider the distribution shown in the below histogram: I have computed a Welch's t-test for a difference in means between these two groups, as well as a Kruskall-Wallis test to see whether these two ...
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### How can I reproduce TukeyHSD's difference of means?

My data set comes from a series of five three-way full-factorial experiments, several of which are unbalanced. The three experimentally manipulated factors have two levels each. I am using R to ...
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### Best way to score pair differences

I'm fairly clueless how to accomplish my goal here... Firstly a bit of back story: I have about 10 technicians, and they each make sets of concrete samples in the field. Each sample has 2 x 28 day ...
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### Adding two outcomes and comparing with a third outcome

I did two experiments, with component A and component B respectively, and the outcome that I have is "mass loss" for those two components. Now, there is a third experiment where both components are ...
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### Hodges-Lehmann estimator as a percentage?

I'm comparing samples X and Y (of sizes M and N respectively). I need to report whether the samples are statistically different (Mann-Whitney U-test) and by how much (Hodges-Lehmann estimator) to ...
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### SEM and group invariance: Can I get modification indices for freed parameters using R-package Lavaan

I'm learning structural equation modeling with R and lavaan package. MPlus (other software for SEM models) can print an output indicating what would the effect if ...
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### Bonferroni correction when comparing sub-group with rest of the group

I am working with 4 machines that test products and record a value during each test. I have ~ 1000 records from each, and some recorded values look like: -0.67, 0.3, 5.7, 2.3, -0.78, 5.2, 5.8, 9, 2.1,...
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### Analysis for two groups tested at two different times

I have a dataset with 50 items divided in two groups: placebo (P) and diet (D). Each group has 25 items. Items were weighted once at two different times: at t0 (before treatment) and t1 (after ...
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### Validity of conclusion of statistical tests when comparing two groups of observations in an experiment

I am just reading the results of an experiment, and I am having a hard time estimating their validity. In the experiment, several participant had to perform a certain task twice, once with the ...
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### Am I violating assumptions of mixed effects model?

I am using a mixed effects model to analyse data, but am unsure whether I am committing any violations due to the nature of the data I have. My data comes from a game whereby people have to identify ...
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### Comparing multiple mean scores using t-Test

Situation: Comparing mean scores of level of satisfaction across multiple institutions and overall. Let's say there are 50 institutions, all with different sample sizes. Level of satisfaction is ...
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### How to handle regression with unequal sample size and variance?

Let's say that I have 10,000 people do a study, and in this study they have to spot a bird in a scene as quickly as possible. There are various possible birds that may be presented to each person, and ...
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### Principal component analysis with non-independent observation

I have observations with 6 individual-level characteristics from 2000 units in 56 groups (villages). I know that within groups, characteristics are strongly related as individuals influence each other....
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### What is the difference between doing a linear regression and exhaustive descriptive statistics?

I'm doing a report of the differences between women and men in their performance on a test with variables like: age, education, race and of course genre. I have two options: doing a linear regression ...
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### How to deal with dropouts from a waiting list control group?

Many treatment studies compare a treatment group with a waiting list control group, for example to adjust for spontaneous remissions. Unfortunately, many more participants drop out from the waiting ...
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### Difference in differences in proportions statistical test

I am running a case-control interventional study where the dependent variable/ outcome is a proportion. The cases were given an intervention whereas the controls were not and measurements were taken ...
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### Compare in-pairs differences to between-pairs differences

I have some numerical data which comes in pairs. I need to test the hypothesis that values inside pairs are more similar to each other, than to other values in the sample. Is there a test for this?.. ...