# Tagged Questions

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

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### Is it possible to compare 2 groups while controlling for something?

Is it possible to compare two groups (e.g., t-test, Wilcoxon, Mann-Whitney test, etc.) while controlling for something? E.g., I want to compare home ownership between military veterans and non-...
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### statistical test for analyzing survey data

One question of my survey (n=468) was to indicate on a scale from 1 to 5 how well they know our government. My hypothesis is that women know our government better than men. What statistical test do I ...
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### Comparing the degree of similarity between groups

I have three groups A, B and C and I want to prove that similarity between group B and group A is significantly higher than between group B and group C. How to prove it? Simple example: I have ...
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### 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 ...
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### Difference in mean change between groups - which statistical test to use?

I have three groups for which I have baseline and final measurement values (and intermediate, but that doesn't really pertain to this question). I want to use a statistical test on the mean change ...
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### How to test group differences when elements within a group are not independent?

I have 4 groups. Each group contains scores for items collected at different time stamps from a real-time system. Here is some dummy data: ...
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### How to group/cluster similar words

Let say I have a list of words, such as: apple apale aaple apples oranges ornnges orange orage melons meeons meeon melon melan I want to group them based on ...
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### Minimal Detectable Change for population surveys

I am wondering if it would be possible to calculate the Minimal Detectable Change when examining 2 population surveys? I know how to calculate the MDC in a test-retest situation in which every ...
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### How to compare the results from two time points in the changed group?

I’m conducting a longitudinal experiment. The purpose of the experiment is to detect relation changes among the members of group (actors). At start time point, $t_0$, I formulated some social network ...
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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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...