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Questions tagged [group-differences]

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

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10
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2answers
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 ...
9
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3answers
16k views

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 ...
6
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4answers
19k views

Comparing two binary variables of unequal sizes

I measured a binary variable from two different populations, and now I'm trying to find out whether the different populations differ with regards to this variable. I could use a Chi-Square test, but ...
4
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2answers
3k views

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 ...
14
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2answers
47k views

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 ...
6
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2answers
2k views

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 ...
3
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2answers
13k views

How can i calculate the 95% confidence interval of an effect size if I have the mean difference score, CI of that difference score

Mean difference: 3.7 CI(1.4-6.0) Cohen's d=0.4 how do i calculate the 95% CI of this effect size?
5
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1answer
9k views

Chi-squared test when two vectors have different lengths

I want to compare two groups (vectors) having different lengths to see if their distributions differ considerably. However, when I use chisq.test, I get an error ...
2
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2answers
2k views

How to interpret Mann-Whitney's statistical significance if median is equal?

Testing the difference between the observations of two groups by using Mann-Whitney Test has given the following output (from minitab): ...
1
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1answer
118 views

How can I use likelihoods to compare these three groups? Should I want to do this?

EDIT: Perhaps I should also note that my initial attempt at analyzing this data used a hierarchical model in rJAGS sampling the means from uniform distributions and variances from gamma distributions ...
18
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5answers
2k views

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 ...
5
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2answers
7k views

How to determine the cut-point of continuous predictor in survival analysis, optimal or median cut-point?

everyone! I want to do overall Recurrence-free survial analysis for one continuous predictor with Kaplan-Meier method, but the determination of the cut-point for groups really confused me. Most ...
9
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2answers
188 views

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 ...
2
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1answer
593 views

Overview of concepts of the methods that this Single-Cell Differential Expression (SCDE) tool uses?

I'm unsure about how this tool works, but as I understand it, it tries to use Bayesian probability in order to differentiate the two different groups from each other as well as some other methods. ...
6
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1answer
1k views

Should I re-center variables when looking at moderator effect in men and women separately?

I want to see if an interaction variable in a multiple regression is significant for the whole sample, and then just for men and just for women. When I created the interaction variable for the whole ...
0
votes
1answer
581 views

Difference between normality of residuals vs normality in each group.

I've been searching on the internet and books for quite a long time now and have come to the conclusion that normality of the residuals (each values minus the mean of each group) is the same as ...
5
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2answers
200 views

Claiming validity of a study's negative finding

For a disease that I am interested in, five or six published works of research have shown an association of changes in gene expression with presence of the disease. However, all these diagnostic ...
4
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1answer
208 views

Approaches to compare differences in means with differences in proportions?

I have summaries of hundreds of variables for two populations. Most of these variables are counts, but some are continuous. For example, if I had population sizes $N_0 = 20000$ people and $N_1 = ...
3
votes
1answer
2k views

Data transformation and confidence intervals for mean difference

I have a between-group independent variable with two level (A and B) and a dependent variable Y that I transformed in order to normalize the distribution of the residual. I used a Box Cox ...
3
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4answers
1k views

Grouping samples by clustering or PCA

If I have 5 binary variables with values for 100 observations to give me a 5x100 matrix. ...
2
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1answer
519 views

Jonckheere-Terpstra test: two-sided and one-sided, directed and undirected hypotheses

I need to perform a Jonckheere-Terpstra test, but I am not sure how to do it and how to interpret the results. I have following data: Three groups doctors1, doctors2, doctors3 And how often they ask ...
1
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2answers
983 views

How to compare two non-randomly selected groups within a sample?

I am quite new to Statistics, so please do not flame me for such a simple question. I made a controlled experiment and successfully gathered the data. 41 persons participated. They made a ...
7
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2answers
977 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?...
5
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3answers
860 views

How to compare two groups on a measure of social skills that includes 5 subscales where each subscale is number correct out of 12?

I have two groups of participants. Each group contains 30 children (15 girls and 15 boys). The first group has been sampled from a population of children being raised under some kind of constitutional ...
3
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1answer
389 views

Statistical differences between two hourly patterns

I have 2 groups of subjects, namely: Subjects that are younger than 67 Subjects that are older than 67 Each subject of each group wears a sensor that estimate the metabolic equivalent of tasks (METs)...
2
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1answer
158 views

If one group's mean differs from zero but the other does not, can we conclude that the groups are different?

I have many pairs of measurements. A paired-samples t-test on these produces a 2-tailed p > .1 (so non-significant by typical alpha values). When I run two separate one-sample t-tests comparing ...
2
votes
1answer
958 views

Should I use ANOVA or MANOVA for repeated measures experiment with two groups and several DVs?

I have data on two groups of subjects. Each group was measured three times, and there were four dependent variables all measuring the level of fitness (score of a person's heart rate in five stages ...
2
votes
1answer
490 views

Is it typical for group means of composite z-scores to have means with values of the same magnitude but opposite signs?

I developed a composite score by converting four items to z-scores, then I summed up the z-scores to form a composite measure. However, when I've calculated means to compare finding for two ...
2
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0answers
92 views

Can I fit a linear mixed effects model to these grouped data?

Data and Objective The data are about lane change maneuvers. I want to predict the lane change duration of a driver of certain age and gender. Following is a very small subset of observations and ...
2
votes
1answer
1k views

test for difference between two differences (proportions)

I have 4 independent samples. Two groups A and B measured on time1 and two groups A and B measured on time2. For every group I calculate a proportion. I would like to compare the difference between ...
1
vote
1answer
266 views

Is two-factor ANOVA without replication appropriate for my application?

I want to analyze results from a computer simulation in which I will vary two factors: (1) fan location, and (2) fan flow rate. After the simulation, I will query the results for gas concentrations ...
1
vote
2answers
249 views

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 ...
1
vote
0answers
52 views

Comparing the means of two groups when a large number of data points have the same value

I have data on the profitability of wagers made according to two different strategies. One strategy was to bet $1 on the underdogs in each of a sequence of sporting matches. They have data like this: ...
1
vote
1answer
1k views

How to separate groups using PCA?

I have two groups: A) controls: $25\times2000$, B) patients: $12\times2000$. Group A has ...
1
vote
2answers
113 views

Comparison of two populations by analyzing the dependence of a single dependent variable on several independent ones

I am looking at two populations on which I have measured 4 independent variables ($X_1$, $X_2$, $X_3$, $X_4$) and one dependent variable ($Y$) along with each measurement or observation. I suspect ...
1
vote
1answer
338 views

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 ...
1
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0answers
311 views

getting rid of the batch effects

I have a two data set one with $n=15$ another with $n=25$. Each set of data has around 90 variables. The data collected was experimental so when I try to combine my two datasets I see clear ...
1
vote
1answer
42 views

Estimate group averages

If I have 100 numbers from two separate groups $X$ and $Y$. How can I manually estimate or derive an algorithm to automatically estimate $AVG(X)$ and $AVG(Y)$? I know all the numbers, but I don't ...
0
votes
2answers
111 views

Compare regressions among more than 2 groups

I would like to know if there is a way to compare the relationship between a factor (length) and a response variable (lipid content) among multiple groups? I have given up on ANCOVA, as length is ...
0
votes
2answers
2k views

Comparison of differences between pairs of samples of unequal size

I have four samples $x_1, x_2$ and $y_1, y_2$ with $n_{x1} \neq n_{x2} \neq n_{y1} \neq n_{y2} $. I calculated, using a Wilcoxon rank sum test, that $x_1$ is significantly different to $x_2$ and $y_1$...
0
votes
1answer
39 views

Whether there is significant difference between two gender groups

A data set contains 5 columns: There are 16 people in the dataset(using subjectID to identify them). Each year, when these people were ages 11, 12, 13, 14, and 15, they provided us a score $y$. We ...