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

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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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19 views

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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39 views

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?.. ...
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29 views

Set of 3 binary logistic regressions versus a single multinomial regression

I have reviewed these posts here and here. I'd like to ask a slightly different question about using a set of binary logistic regressions instead of a single multinomial regression. I am using ...
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23 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 ...
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38 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 ...
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12 views

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 ...
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1answer
10 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 ...
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26 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 ...
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21 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 ...
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18 views

Percentage of variance explained by a given variable

I have two groups A and B which differ on a given characteristic X. X is binary and can only take two values, let's call them (T,F). 15% of individuals from group A ...
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10 views

Comparing Groups

I am using SPSS, and I cannot figure out the best way to compare my groups. My problem is that I have various groups, like mental health diagnoses, and I have collected data on events which took place ...
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13 views

Two groups: first with one measure, second with two measures: how to test between group difference?

In my research I have two groups: 1) Healthy group 2) Patients with disease I have a variable (quantitative) that measures some skin property for each patient. But diseased patients have two types of ...
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49 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 = ...
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14 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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1answer
54 views

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 $$H_0: \mu_1 = \mu_2$$ $$H_0: \mu_3 = ...
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15 views

Methodical questions about multiple group comparison and power

I want to compare 5 groups with different sample sizes (1 control, 4 patient groups) with regard to one independent variable. I want to compare all patient groups against one (larger) control group ...
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2answers
133 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 ...
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8 views

Characterizing hour-to-hour differences and against a mean

Assume that I have a dataset that shows the number of foosball games that a trainee has played per hour in an 8-hour day of practice (assume games are brief and there is no limit to the number one can ...
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158 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 ...
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7 views

how to define which of measured, non gaussian variables are effective in discriminate given groups?

I have eight groups (100 samples each) and 43 evaluated variables, with different distributions (some of them are right skewed, some left skewed, some with many zeros etc.). I'm trying to understand ...
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21 views

Best method of analysis for 2 independent groups for multiple tasks before and after treatment?

I have two independent groups at the start of the study. Both groups went through the same study procedure where they went through multiple tasks (not necessarily repeated measures). They were then ...
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10 views

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 ...
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225 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 ...
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25 views

Is it possible to estimate SD from two known means and SDs (preop vs. postop.)?

We're working on assessing the efficacy of surgical treatments for a given condition through a systematic review with metanalysis. In order to create the forest plot, the stat guy asked us to provide ...
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9 views

comparing proportions in multiple age groups

The hypothesis is that with increasing age the occurrence of ovulation is more frequent. I have binary data (ovulation / no ovulation) for four age categories in cats, some of the individuals may show ...
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18 views

3 groups, 3 measurements for each, three replication

I'm very new in the field I'm working now and have a simple question: I have three different groups, e.g., old, young and kid. These properties (like, weight, height and heart beats) are measured in ...
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12 views

Comparing differences from mean against whole group mean

I am looking for a measure that will allow me to compare the difference in means from year to year in a sub group compared to the whole group differences over the same time frame...I could do repeated ...
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19 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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12 views

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 ...
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1answer
35 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 ...
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7 views

Compare related time-series count data before and after intervention

For a university library we did an intervention to create more free seating spots for students by introducing a way for students to temporarily give up their spot while away. They did this with an ...
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35 views

What statistical test should I use to compare the binary outcome of two groups (with pre- and post- test)?

I have two groups of people: experiment group and control group. People in each group accepted pre-test and post-test. The outcome of the tests is binary: "good" or "bad". In other words, each people ...
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40 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 ...
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25 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 ...
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29 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 ...
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11 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 ...
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1answer
71 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 ...
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43 views

Plotting many groups tested with many experiments

I have 1 control group and 9 treatment groups. The 10 groups are tested against 13 treatments (with each have 3 variations so a total of 39) and results are collected. How to plot the results in as ...
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1answer
22 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 ...
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90 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): ...
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1answer
70 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 ...
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17 views

How to assess difference between two groups

I am a newbie in analysis of transcriptomic data and I've encountered some problems. I have a data set, where are two groups of samples (7-8 samples in each group). I would like to define if there is ...
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19 views

How to analyze whether there are significant differences between 2 groups in samples (with 4 characteristics)?

I am stuck in analyzing my own data for my bachelor's tesis. I have 1 IV,1 DV, 1 mediating variable and 2 moderating variable (all items used Likert Scale), and 4 control variable which are Tenure, ...
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50 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 ...
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7 views

Integral formula for differences in means between groups

BACKGROUND: I was fascinated by the discussion on this post discussing the issue of interpreting the meaning of confidence intervals versus credible intervals, as well as their calculations. In an ...
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1answer
62 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 ...
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1k 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 ...
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80 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 ...
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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 ...