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

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Differential Expresion Comparisons

In a Differential expression experiment concerning a gene of interest there is an upregulated condition, downregulated condition and control. When comparing these, it obviously makes sense to compare ...
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What is the null distribution of the between-group variance?

Scenario From a population, we randomly sample $n$ individuals, measure the normally distributed random variable $X$ and compute the total variance $V_T$ of $X$ in this sample. Then, we randomly ...
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How to treat subsamples that differ in respect to the dependent variable prior to any treatment?

I have conducted an experiment on a sample that consisted of both male and female students to see if a specific emotion influences moral judgment. My research goal didn't involve any hypothesis about ...
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21 views

How to analyze differences between two time series collected under two different conditions

How should one analyze time series data that were collected during two seasons: season 1 and then at season 2, where during each season a measurement sample for several continuous variables were ...
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9 views

comparisons of means within grouping factor (after two-way ANOVA)

Let's say in each of ten very different schools, one half of students is offered free lessons in physics and the other is not. After the next examination phase, the physics skills of the two groups ...
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11 views

Convenient plot size detectable difference vs Least Signifcant Difference

I am curious how Hatheway's (1961) Convienient plot size calculation, once rearranged to solve for the detectable difference, relates to a standard LSD calculation: $$ d^2 = \frac{(t_1 + t_2)^2 \times ...
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16 views

Standardized difference of means for multiple classes

Standardized mean difference is very straightforward when you have 2 distributions / groups. How is this metric computed when you have >2 groups? Is there a better alternative to determining the ...
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10 views

single value to describe separation between 3 or more classes

I want to optimize a pre-treatment process. The optimization should be driven by a cost function that describes how well several groups (between 3 to 6 in fact) are separated, after the pre-treatment. ...
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9 views

model severity vs duration of disease load

I have been thinking about this for some time now and still not sure how to analyze it. So hoping that someone here could give me some hint. We are measuring disease load continuously (ranging between ...
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Comparing capture rates in 2 groups: which test?

I am comparing rate of capture (animal captures per hour) between two years. I'm interested in determining whether there is a difference between rate of capture between the two years. A survey night ...
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37 views

Permutation test for equality between the distribution of $g$ population

I have a data matrix of 42000 observation and 12 variables I suppose to observe 12 samples of size $n_j$ from 12 indipendent random variables $Y_j,j=1,...,g$ I want do a permutation test for $$H_0: ...
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60 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 ...
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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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40 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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31 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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26 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,...
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47 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 ...
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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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36 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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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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20 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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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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1answer
51 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,...
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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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55 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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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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300 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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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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185 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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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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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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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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227 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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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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20 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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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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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 ...
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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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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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51 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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52 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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27 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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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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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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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 ...