Questions tagged [group-differences]

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

438 questions
68 views

How to compare three groups ranking a set of items?

I have six photos which the test subjects rank according to their preference. So the response per person is six columns, "Rank of photo A" to "Rank of photo F". I am grouping the subjects by religion,...
859 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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Demonstrating whether two groups of participants can be grouped together

I have two sets of data from two groups of participants that are identical in all but one way: one set of data were collected using software A and the other set was collected with software B. It's ...
45 views

Compare random samples and make inferences about difference in distributions

I have a general question about comparing independent samples of continuous data and making inferences about difference in distributions. I'm really struggling with which approach to use. Besides of ...
185 views

How to calculate cohen's d (and CI) for survey data

I am working with the TIMMS and PIRLS data. Both data sets use a Jackknife repeated replication design. Both data sets also use 5 plausible values for each student's grade (5 values with different ...
69 views

How do I test for a difference in the standard deviations of two groups?

I have two groups and I want to know if there is a difference in standard deviation (or variance if it's easier) for each parameter. Here is a table of descriptive statistics for my data: After ...
180 views

Mean Differences in Poisson Regression

I performed a Poisson regression. My dependent variable is number of days and my independent variables are all binary indicators (e.g. facility = facility1 facility2, facility3 and severity = extreme,...
18 views

selecting statistical test

I wish to analyse data regarding physical activity levels of a population (unaware yet if it will be parametric or non parametric) at baseline, week 12 and follow up at three months. My research ...
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Reject $H_0: \mu_1 = \mu_2 = \mu_3$ but not $H_0: \mu_1 = \mu_2, H_0: \mu_3 = \mu_2,$ or $H_0: \mu_1 = \mu_3$?

Is it possible to reject $$H_0\!: \mu_1 = \mu_2 = \mu_3,$$ for example, with an F test in the context of an ANOVA table, but not reject any of the following: \begin{align} H_0\!: \mu_1 &= \mu_2 ...
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 ...
2k views

Statistical tests for uneven groups

We performed an experiment (usability testing), which had two independent samples, one group with 5 participants and the other with 24. Based on the analysis of the distribution of the data (Shapiro-...
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Standard deviation of sample mean differences used as the basis for calculating standard error of the two samples

I came across this problem in the OpenIntro Statatistics (it is very free) textbook: Now, in calculating the t-statistic for the difference of means, the same book shows that the Standard Error in ...
267 views

Check for significant difference between numbers of sightings per cardinal direction

I have data in a form like this: quantity direction 10 n 5 e 6 ne 12 n 20 nw 5 s 8 n 1 sw 3 se 2 ne 6 nw 8 n 2 se 3 e 4 w 9 nw The information behind these ...
52 views

What is the appropriate statistical test to perform a difference of means within a difference of means?

Let's say I am interested in measuring the effect of three different types of interventions on test scores. Let's say the intervention is book quality, of which there are three kinds of book quality (...
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Comparing Performance and Determining Scaling

My understanding of statistics is fairly basic, but I'll try to be precise here. Method X of doing something exists and can be timed with a particular method of ...
46 views

Grouping usernames/emails in a data set

I have a column in a dataset that is the 'user'. Can look like this: tom green tgreen tomgreen@here.com sam blue samtha green How do i get this to group this so that the first three are grouped ...
199 views

ANOVA (assuming different distributions) vs Kruskall-Wallis and post-hoc tests

During stats courses on Uni I learnt (if I remember correctly and hopefully don't put my teachers to shame) that if you want to compare multiple groups with eachother you look at the residuals of an ...
39 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 ...
75 views

Cluster two feature samples with no knowledge of the number of clusters

Thanks in advance for the help I have around 13000 samples with two features each and I would like to cluster these samples into groups. A few caveats. One, I don't know how many groups there are (...
27 views

Standard effect size for assuming equal means

I do a community survey on a website once each year, I have data from the past two years and this year I'd like to remove questions which are getting similar answers each year. The survey questions ...
683 views

T-tests, manova or logistic regression - how to compare two groups?

I'd like to check whether women and men differ on those five variables, that can be correlated with each other. The groups are also not equal with 589 females and 293 males. The solutions that come ...
32 views

Conditions for groups in independent samples test

I wish to conduct an experiment where I have a number of different groups, let's say four groups of X people each. Each person in each group partakes in a similar experiment, with each group testing a ...
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): ...
4k views

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 ...
589 views

MANOVA or Mixed ANOVA? Several measures as dependent

I am trying to analyse data of 2 different groups (control vs experimental, brain damage) and their performance on 3 different cognitive tests (the results of which are not correlated) to determine ...
1k views

Is it possible to normalize data by different group leaders separately?

I have a dataset that contains different states of a country. In every state there are different companies and one company in every state is manager of other companies in that state (other companies ...
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 ...
17k views

Compare t-test of difference in means of 3 samples

I am comparing the statistical significance of the difference in means (say average age) using three samples (say classes) a, b, and c. The results of t-test show that there is no significant ...
634 views

how do I compare percentages and show they are significantly different?

Here is my data: I have two groups (experimental group and control group)voting for 6 different actions, listed as A, B, C, D, E, F. The sample size of the 2 groups are different. Therefore, I am ...
350 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)...
35 views

Testing for significant differences in populations from one sample

I have a data set with population information for 6 age groups. In theory, I wish to know if a specific two of these age groups are different from each other. My first question is: Can I subset the ...
39 views

Which statistical model/method should I use?

I have a data collected in New Jersey, and the units are individuals nested in four cities. Within four cities, there are also three types of neighborhoods defined by someone. I am trying to see if ...
59 views

Repeated-measures while comparing groups

I've been reading up on related posts, however I'm still confused as to how to choose the appropriate test to analyse a repeated measures variable, while also comparing two groups. The situation is ...
1k views

Mann-Whitney with many zeros

I'm running a basic Mann-Whithney U test in R between two groups; each group represents the abundance values of a particular bacteria within an animal. Therefore a 0 means that bacteria is not ...
26 views

correct statistic method

I would like to ask about correct statistic method. We did an observation of wild population animals in a specific place. We observed that species tend to group differently. We created a 5 size ...
202 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 = ...
578 views

Comparing unbalanced groups with ANOVA/Kruskal-Wallis when one group has only 1 observation

I would like to compare a continuous variable across 5 health status groups, but one of the groups has only 1 observation. Would an ANOVA/Kruskal-Wallis be valid? What can I do about the group with ...
1k views

Friedman test for a repeated measures experiment with replicates

(Please see example with reproducible data at the end) I have a data file with the results of an exercise performed 16 times with each of 2 control devices by 3 subjects. I measured the task ...
83 views

Group wise imputations allowed?

What is the correct way of imputing missing values? We are trying to predict the label of persons belonging to group A or B. The alternative hypothesis is that there are differences in parameters for ...
150 views

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-...
53 views

Measure how different are two groups in their answering on 25 ordinal variables

The research context: I'm interested in usage frequency of special interest websites and its predictors. I asked individuals (n=1000) for the usage of 25 different websites in 25 items in a survey (...
94 views

How to detect different social groups in a small questionnaire dataset?

I work with a very small questionnaire dataset, in which perception of 10 respondents to the size of, say, an unseen population is quantified: The population is divided into eight sub-populations, and ...
240 views

What statistical analysis should I use for this (attached) dataset?

I have a dataset of 815 positive examples and 9492 negative examples for a certain class. Each example is represented by 12 features and a target label (i.e. TRUE/FALSE). The dataset is in a CSV file ...
520 views

Difference between regression between groups vs across all subjects (continuum)?

I'd like to understand this better in terms of drawbacks and suitability. For example, if my data includes investigating differences between 2 patient groups and a control group (3 groups in total), ...
96 views

Linear trend for correlations

I am evaluating three independent samples (1-3). For each sample I have calculated a correlation of variables A and B. I am now interested if there is a linear trend in the development of the ...
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 ...
887 views

Comparison between groups with one group normally distributed, and the other skewed

I want to compare continuous numerical variables between two groups. Sample size is small (27 for one group and 43 for the other). I use Shapiro-Wilk test to check for normality of distribution of ...
827 views

Comparison of ratios between multiple groups

I need to perform statistical analysis whether there is any difference in the usage of each gene version between disease groups. I have 3 groups, in each group there is a different no. of patients. ...