# Tagged Questions

Procedures that rely on relatively few assumptions about underlying probability distributions.

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### Should I remove the outlier?

I want to run an ANOVA test. I am therefore testing for normality. I have tested each group and the residuals (group together)for normality. My data sample does not look approximately normal. However ...
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### Is this close enough to be normally distributed for using a parametric test?

Can I say that the values are close enough to be normally distributed? The histogram does not look normally distributed at all, but the Q-Q plot is not so far away. My sample size is 30. The shapiro-...
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### 1-way vs. 2-way Anova (or non-parametric tests)

I am new to statistics and ecology and am doing this data analysis for bird count data. We have 3 treatments (which is 1 factor with 3 levels) and 2 sites (which are considered replicates as per ...
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### Non-parametric estimation of error distribution in regression

Consider the following model: $y = 1$ if $g(X\beta) + u > 0$ and $y=0$ otherwise where $u$ is $iid$ according to some distribution function $F$. I want to recover the distribution $F$ without ...
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### Bootstrapping a Kernel Density: Help in interpreting R code

I found this excellent code snippet online which gives the code for boostrapping a kernel density estimate to get confidence bands. Now, I am not that well versed in R, and would like to know what's ...
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### Why did two meanings of the term non-parametric arise?

There are two meanings for non-parametric: Non-fixed number of parameters Distribution-free assumptions How did this happen? Was it due to two communities diverging? It is sometimes confusing to ...
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### Spearman's Rho/Kendall's tau with Dichotomous variable

Is it appropriate to use Spearman's rho or Kendall's tau to find the correlation between a dichotomous variable & a continuous variable? My data is non-normal, has outliers and unequal variances. ...
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### What nonparametric test should I use?

I am having two groups of data (unpaired, different sample size N) that I need to compare in non-parametric way. I would like to use median. I read about median test, but I am not sure if that is the ...
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### Nonparametric Correlation with Dichotomous Variable [duplicate]

I have a continuous variable (total cholesterol mg/dl) and a dichotomous variable (gender). I want to see whether a relationship exists between the total cholesterol level and gender. The data is ...
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### Testing for a statistically significant difference across multiple categories with ordinal data

I have ordinal data from a single reviewer who ranked the quality (and other factors) of 66 reports. 19 of these reports were about mining, 10 about Waste, 10 about Infrastructure, 9 about transport ...
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### Partitions, and Random variable indexes in Dirichlet Process

I am going over this tutorial and am confused by the notations on pages 14 and 15. Here is my understanding for the notations on page 14: $G\sim DP(\alpha,G_0)$: Means $G$ is a draw from a DP, with ...
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### Post hoc non-parametric tests

I am analyzing some data that has violated assumptions of ANOVA and am using the WRS2 package in R. I am concerned about the post hoc tests. I am comparing three groups, Dx, (schizophrenia, ...
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### Is there a nonparametric test available in R to analyze serial dependencies for short time series?

I am developing a small web application with R and the Shiny-package to conduct easy analysis of single-case time series data. For this purpose, I need a nonparametric test that allows to analyze ...
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### Non parametric (or parametric) two way ANOVA in case of heteroscedasticity [duplicate]

I've got the following data set: 2 independent variables (age, with 4 levels, formulation, with 2 levels) and 1 dependent variable (consistency of cheese slices). I've tested the ANOVA assumption of ...
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### Non-parametric estimation of competing risks model with unobserved heterogenity

I've been searching for a while if there's an R package that allows to do non-parametric estimation of a competing risks model with unobserved heterogenity/frailty. ...
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### How to take random draws of a low-entropy “meta-random” distribution

I'm working on a simulation study, and for it I'd like to be able to generate random draws from a random multivariate distribution. I'm looking for something pretty chaotic, in the sense that it's ...
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### Is there a non-boostrap way to estimate confidence intervals for Kernel regression predictions?

Simple problem of estimating: $$y = f(x) + \epsilon$$ Where I use your standard Nadaraya-Watson Regression to guess $f(x)$. This is relatively fast and works well even in an online setting. Now I ...
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### Kendall W for continuous data

Simple question: can I use the Kendall W test for continuous data? Cuz I used it for a bunch of continuous variables and almost all coefficients are very close to 1, with p-values very very very small ...
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### Which nonparametric test should I use

I am currently doing an experiment to test whether there is a significant difference between test results of a control group of steel bars of good shape and another group of corroded steel bars. I do ...
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### what test to use for comparing count data across multiple groups

I have five groups of students and 40 in each. And we counted the number of references spelling mistakes in their homework. We would like to compare to see if there exists any groups differences in ...
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### Testing for Stochastic Dominance - Mann Whitney with Unequal Variance

I've been looking for methods like Mann Whitney, but without homogeneity of variance. So far, I found that I suppose to test for stochastic dominance instead - i.e. modifying the null hypothesis. ...
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### Choosing evaluation measure for non-parametric clustering

I have to cluster some data using non-parametric clustering technique which is given in this paper. After all the cluster evaluation measure used in this paper is Normalized Mutual Information as they ...
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### Comparing huge data sets that are non-normal and different lengths in R

I'm comparing two data sets. Each set is extremely large, about 25,000 quantitative pieces of data in length. I want to find if these sets are significantly different, but the problem is that they are ...
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### Density estimation for large dataset

I have a unidimensional data set with more than 1000000 observations. Assuming that those observations are independent realizations of the same random variable I need to estimate the underling ...
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### Equivalent to Spearman correlation for non-monotonic data

I have several datasets of independent variables that have a monotonic (but non-linear) relationship. If I want to assess if they're correlated, the test of choice is Spearman's (rho) or Kendall's (...
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### what test should i use to find the difference of variable based on service tenure?

i have 3 variable which is understanding, motivation and attitude (Likertscale). i want to see if there is difference of service tenure towards these three variable... what test should i use? my data ...
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### Is Cronbach's alpha a parametric or non-parametric test?

Is Cronbach's alpha a parametric or non-parametric test? I need to know more specific details about it.
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### Mann Whitney U test with normal distribution approximation: null hypothesis rejected?

I'm new with U test and I have some doubts about the rejection of the null hypothesis with the U test with normal distribution approximation. In my example I used this data for a 1 tailed test:  ...
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### Likert-type mediation on non-normal/non-linear data

I have collected data from a questionnaire with multiple questions, all answer possibilities being on a 5-point Likert scale. After initial analysis, my data does not have a normal distribution nor ...
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### parametric or non-parametric in comparison of a dependent variable within several groups

I am comparing maths and chemistry scores of students in several schools. I am not comparing the schools with each other. I am just trying to say that students do better in maths than in chemistry in ...
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### What are the differences between parametric and non-parametric statistical tests?

I have seen that there are parametric and non-parametric statistical tests. What are the differences between them?
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### Why results from R's wilcox_test and Matlab's ranksum are not consistent?

I found when using two sample ranksum test, Matlab's ranksum gives different p value from R's wilcox_test (seems to be related to unequal sample size), I'm not capable of delving into their ...
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### Prove the relationship between Walsh averages and Wilcoxon signed rank test

In my lecture notes it is stated that sum of all positive signed ranks (defined in Wilcoxon signed rank test) = the number of Walsh averages that are greater than median How can I prove this ...
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### If the Epanechnikov kernel is theoretically optimal when doing Kernel Density Estimation, why isn't it more commonly used?

I have read (for example, here) that the Epanechnikov kernel is optimal, at least in a theoretical sense, when doing kernel density estimation. If this is true, then why does the Gaussian show up so ...
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### chisquare outlier test assumptions

what are the assumptions of the chisquare outlier test? ( in R: chisq.out.test()) Is it only applicable if the data follow a certain Distribution? What is the idea of ist Definition of outliers? ...
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### Rookie question about non parametric and parametric tests

I am a very rookie statistical test user and I want to better understand how to choose between a non parametric and parametric test based on my data. I read several statistical tests tutorials but I ...
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### Bootstrap comparison of group means instead of ANOVA/tukeyHSD

I have several groups (~30, >100 data points per group) and would like to see if there are differences between the group means and where. Both ANOVA and Kruskal-Wallace say yes and I'd like to see the ...
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### Permutation test for repeated measures (in time)

I have the measurements of a quantity, observed every day for 60 days Usually, this quantity is really near to 0, apart from 3 days where it is (significantly?) greater than 0 I thought it would be ...
10 views

### How to assess the significant level of a sample difference per number of element

I have 3 samples of 28 paired elements which have been tested for normality and they are not normal due to biomodal distributions. I carried out a Friedman test and is not significant. However I know ...
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### When to use Median test and Mann-Whitney test?

I know that both uses to find whether the two sample medians are equal or not. But I want to know when should I use them? Under which conditions these two tests can be applied separately?
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### Dunnett T3 test interpretation

i have result from a Dunnett T3 test using package DTK in R. The result do not give me any p-value but only "Diff", "lower CI" and "upper CI". i can understand the difference between groups as the ...
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### How to test an interaction effect with a non-parametric test (e.g. a permutation test)?

I have two categorical / nominal variables. Each of them can take only two distinct values (so, I have 4 combinations in total). Each combination of values comes with a set of numerical values. So, I ...
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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 ...
366 views

### The correct way to display non-normal data?

In my university we learned a lot about normal data, but handling non-normal data wasn't really covered. For some benchmarking of an application I have data has a very high frequency around one value ...
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### Maximizing a non-parametric Probability Density

Assume we have a set of samples and estimate the underlying distribution with a non-parametric density estimator like the Kernel Density Estimator. Lets assume with a gaussian kernel. In my case it ...
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### Non-parametric paired data: several Wilcoxon signed-rank tests? Other?

Scenario: I've taken blood samples from a group of patients (n = 15) and measured the expression of one marker on three cell populations within each sample (transitional B, naive B, memory B). I'm ...
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### p-value interpretation of Jonckheere Terpstra:one-sided or two-sided

I am using the Jonckheere-Terpstra test in order to validate the pooled t-test results. Basically, I like the JT test because of its non-parametric nature. Basically, I am now trying to understand ...
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### Non-parametric analogue of a one-way MANOVA

What is the best test to perform a non-parametric multivariate analysis of variance? I have 4 levels of 1 factor, $n=60$ statistical units and 30 dependent variables.