Questions tagged [group-differences]

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

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What is effect size… and why is it even useful?

I have an introductory-graduate-level statistics background (assume I know mathematical statistics and probability at an undergraduate level (e.g., Wackerly et al., Ross' Probability), and have some ...
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Unequal sample sizes: When to call it quits

I'm peer reviewing an academic journal article and the authors wrote the following as justification for not reporting any inferential statistics (I deidentified the nature of the two groups): In ...
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Comparison of ranked lists

Suppose that two groups, comprising $n_1$ and $n_2$ each rank a set of 25 items from most to least important. What are the best ways to compare these rankings? Clearly, it is possible to do 25 Mann-...
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10 % false positives from nonlinear mixed effect models : Why? [closed]

I've run a simulation study in order to estimate type I error rate of the test of group effect in a nonlinear mixed effects model, using nlmer from lme4 package. The results show there is 8-10 % false-...
3k views

Compare the statistical significance of the difference between two polynomial regressions in R

So first of all I did some research on this forum, and I know extremely similar questions have been asked but they usually haven't been answered properly or sometimes the answer are simply not ...
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How to test whether subgroup mean differs from overall group that includes the subgroup?

How can I test whether the mean (e.g., blood pressure) of a subgroup (e.g., those who died) differs from the whole group (e.g., everyone who had the disease including those that died)? Clearly, the ...
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Investigating differences between populations

Say we have a sample from two populations: A and B. Let's assume these populations are made of individuals and we choose to ...
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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 ...
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How to compare ranked data?

I have some questions about how to analyze ranked data. The data looks like this: 4 groups of people with HIV and 16 other groups of people living in the same village were asked to rank 12 ...
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conditional difference between 2 uniform random variables. Surely Breiman can't be wrong?

I've already searched and don't find this particular case in XValidated. Statement: "Electricity is turned on uniform-randomly at a given time of day (in 24 hour window). Once it has been turned on, ...
233 views

Are these populations non-random and different?

What would be the simplest, straightest-forwardest way to determine the following: Whether A,B,C is non-randomly distributed in each single group (IE: are there more A's in group 1 than random chance ...
8k views

Test to prove two means do not have a difference

I have a population that I measure a value from once a day. I then made a change, and continued to measure that same value from the same population. What test could I use to prove that my change did ...
962 views

Cook's distance in detecting outliers

According to my understanding, Cook's distance measures the influence of each observation by excluding points when fitting a model. So I assume it could be an reasonable approach for outlier detection?...
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Principal component analysis with group data

In my experiment I have used 30 different accessions of a species. One group is challenged drought and the other group is control. I have collected data on 6 different parameters. I want to know which ...
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Test whether time of maximum differs across two groups

Suppose I have 10 repeated measurements of a quantitative variable $X$ of the individuals within two groups (let's call them A and B). For each group, I have the estimated means of variable $X$ at the ...
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How to test group differences when neither parametric nor nonparametric assumptions are met?

Consider following example. We asked 50 men and 50 women one question and they answered on 5 point likert scale (1 is completely disagree and 5 completely agree). Suppose that 50 men responded 20 ...
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Assessing group differences on multiple outcomes

I have one independent variable with two levels: Gender (Male and Female), and dependent variables will be composed of three test scores: Impulsivity, Assertiveness, and Social Desirability. My ...
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What is the variance of the standardized mean difference of two independent studies?

I have computed the standardized mean differences for a pair of independent samples. But when I Googled for the "variance of the standardized mean difference" I got rather confusing results, with ...
689 views

Comparing different conditions on a binomial distribution

I have some data where I have tested a binomial random variable under 4 conditions. The null hypothesis is that they all have equal means, alternative hypothesis is that one or more means differ from ...
984 views

Testing for equality of variance in permutations (microarray analysis with bioconductor)

I have measured whole-genome gene expression in two groups of animals, n=6 in each group. My goal is to detect differentially expressed genes - pretty standard analysis. The typical thing to do, and ...
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What is the relationship between differential analysis and hierarchial clustering?

I'm currently in an internship for R bioinformatics, where I'm writing software for single-cell RNA sequencing analysis. We're looking for differentially expressed genes between groups, but I don't ...
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Accounting for groups in GzLM Poisson regression

I am currently trying to perform a regression on data with one predictor and one covariate. The hypothesis I am trying to test is whether the incidence of pores (a hole through a cell) increases when ...
240 views

How to evaluate differences of multiple Likert scale ratings of multiple items within groups?

I have data where different reviewers rated how important multiple topics are on a scale of 1 to 5 (Likert scale). Each of the topics is assigned to a group. I want to see if there any differences in ...
537 views

Nesting and grouping formula confusions using lme

I've seen a fair few of these posts already, and I feel a bit silly for posting yet another question on the topic - but I just cant seem to get my head around it. I'm very new to R and esp new to lme, ...
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Comparing the result of a study which has unequal group sizes

I have conducted two user studies and in my studies I didn't have control over the group sizes. In each study users were put in groups and they were asked to perform some group activities. Here is the ...