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

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Combining data from different locations to test difference in populations

I have (irregularly spaced) times series concentration data for four locations and am trying to discern whether or not there has been a change in concentrations after a particular event. To avoid ...
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1answer
54 views

Rank and z-transform instead of Wilcoxon?

Andrew Gelman in a recent post in his blog suggests using a rank, transforming the rank to a z-score, and then using parametric tests and tools instead of performing non-parametric tests. I never ...
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12 views

Confidence intervals for Kendall's tau-b

I am working on some stats coursework, and have non parametric bivariate data. n=19, so small sample. There are a number of tied ranks, so I'm planning to use Kendall's tau-b rather than Spearman's, ...
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17 views

Nonparametric equal variance tests

I have two large, non-normal samples as evidenced by the Kolmogorov-Smirnov test. I now wish to test for equality of variance nonparametrically. I'm confused as to which nonparametric test is ...
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1answer
33 views

Non parametric: How to detect different groups

I have data sets for different serial numbers of devices. Those data are not following a normal distribution. I would like to know which serial numbers are behaving differently from the overall ...
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8 views

How to determine central ranking in Mallows' model?

I've been trying to read up on Mallows' model, which involves ranked (full, or partial) data. One of the parameters is the central ranking. However, the resources that I have read online do not tell ...
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19 views

Volume for Parzen window and $k_n$ Nearest Neighbors density estimation

In Parzen window estimate, suppose we want to estimate the density at $x_o$, what we do is raise, say a uniform kernel at $x_o$, find number of points falling in the box, which is $k_n = ...
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21 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 ...
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12 views

Comparing parametric and nonparametric models

I would like to compare some parametric and nonparametric methods. I have a small real data set (n=50), Could I use k-fold cross validation and then use some statistical distance measure like ...
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1answer
26 views

Spearman's correlation as a parameter

Spearman's rank correlation for a bivariate sample $\{ (x_1, y_1), (x_2, y_2) , \ldots , (x_n, y_n) \}$ is generally defined as the correlation between the ranks of the observations, but what is the ...
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42 views

Comparing several asymmetric distributions

I have constructed 3 toy distributions using R ...
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1answer
7 views

Detecting outlying distributions of ratio data

I have a dataset consisting of hundreds of repeat observations on thousands of agents. Each observation is a ratio between two distance measures, A and B, where A is always larger than B. Thus, my ...
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1answer
106 views

Difference between LOESS and LOWESS

What is the difference between LOESS and LOWESS? From Wikipedia I can only see that LOESS is a generalization of LOWESS. Do they have slightly different parameters?
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12 views

Choosing to adjust or not after Kruskal-Wallis rejection

I have a series of data (4 numerical variables) and 4 categorical variables (with multiple factors each). I need to test for differences between various subsets based on the categorical variables. ...
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1answer
49 views

Dunn's test p-values in R are exactly half those in SPSS and GraphPad for the same data

Firstly, this is my first post to Cross Validated, so apologies in advance if I have infringed any conventions. I am writing up a PhD thesis on aspects of biomedical research, and use R for my ...
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9 views

Comparing the degree of “spatial clustering” of a response variable across different treatment groups

I have a neuroscience dataset consisting of unpaired data obtained from cells recorded under either control conditions or an experimental manipulation. For each cell I have recorded its spatial ...
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1answer
19 views

Applying a non-parametric ANCOVA to the interactive effects of multiple explanatory variables.

I am having a few issues processing some data in that the number of samples is far less than originally anticipated. In a control and impacted design, there are 11 samples each. I thought this seemed ...
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8 views

what is the most suitable method to compare percentage values if there are no mean (no replicates)

I have a problem with my data analysis part in my final year research thesis. I measured methane generation efficiencies (percentage values) for 3 different biogas reactors for 2 months. But data in ...
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15 views

non parametric analysis of variance in small, unbalanced data set

I'm facing a data set composed of five different dependent (1,2,3,4,5) and three independent (I,II,III) variables. 1,2,3,4,5 are continuous but not normally distributed. I,II,III are qualitative, I ...
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1answer
48 views

Which ones of $n$ random variables have the largest mean (non-parametric way)?

Let us have $n$ random, mutually independent variables $X_1,X_2,\dots,X_n$. Let us have some samples of them such as $x_{i,j}$ where $i=1,\dots,n$. I want to know the maximal variable(s) based on ...
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20 views

permanova or non-parametric test for multiple explanatory variables and interaction

Hi I am trying to find a test to analyse the following data set. Response variable is failure or success (0 and 1) measured over 4 time points, under 2 different treatments (light and temperature) in ...
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1answer
43 views

Non parametric analysis

The my dataset is not normal distributed. In order to apply a non parametric analysis, exist only the Kruskal Wallis test or others? I need to find a test similar to ANOVA to apply a dataset not ...
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19 views

Which test should I use for hypothesis testing?

I have 2 sets of samples that I want to test if they are different or not. These 2 sets are not paired, but they are "related" (explained below). The sizes of the sets are not equal. Which test should ...
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25 views

marginal likelihood in linear bayesian regression (in weight-space)

I want to tune the hyperparameters namely the target deviance $\sigma_y$ and weight deviance $\sigma_w$ in bayesian linear regression. The posterior distribution in level-1 inference which is ...
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8 views

Data analysis method for Tree selection

I need to select the best tree accession out of 350 vegetative propagated tree accessions. First I need to select straightness. Then I need to select for branching from above selected accessions. ...
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19 views

Can quantile regression be used to pool multiply imputed count data?

I am using the mice package in R to impute missing data in small study. The study investigates the effect of a behavioral intervention on the frequency of a particular behavior, i.e., count data that ...
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14 views

Data analysis method for tree selection

I consider 3 qualities of tree varieties; I call them $X,Y,Z$. I first select trees for $X$ character. After that selection will be done for $Y$, with use of trees which are selected for $X$. Finally ...
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41 views

How to test for a correlation between two variables, if the linearity assumption is violated?

I have two variables that show no linear relationship. It's not even monotonic. Does this mean that the variables are independent of each other? Can I still run a non-parametric test? Or can I just ...
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31 views

Non-parametric test for pre vs post between groups and unequal group size

I have pre-post test ordinal level data (likert). Pre and post samples were from the same population, but there was unequal group sizes (less people completed post compared to pre). I have run a ...
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1answer
26 views

Studying the distribution of the p-value?

I have two data vectors $X=(X_1, X_2, \dots, X_n)$ and $Y=(Y_1, Y_2, \dots, Y_m)$ where $X_i \overset{iid}{\sim} P$ and $Y_i \overset{iid}{\sim} Q$, and I am performing a two-sample test (i.e KS test ...
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1answer
33 views

Pairwise non-parametric test for small sample sizes

I was asked to check a small dataset (3 replicates for 5 treatments, each) for significant outcome differences. I give an example: The variance within replicates in the data cannot be assumed ...
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1answer
45 views

Limitations to generalized additive model (GAM)

I don't quite understand the generalized additive model behind the GAM package in R. It seems quite powerful with the ability to easily find complex relationships and confidence intervals for these as ...
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1answer
23 views

non-parametric analysis

I have faced a problem with my data which have different disrtibution. I have some data that are scaled one so possible to do ordinary parametric analysis on them (ANOVA, Correlation, ...) and series ...
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26 views

Multiple comparison of non-normal, heteroscedastic data. What test should I use?

I have a set of brain pathology data. These were obtained by counting certain parameters in the brain. Due to availability of human brains, the amount of cases vary a lot across the different groups ...
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14 views

What is the correct measure of significance to use on a small non-normal mixed data set?

I'm trying to run statistics on a small data set that does not have a normal distribution (possibly due to size of sample). I'm trying to work out if the sample group has any effect on the result ...
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15 views

Is there a stats test to compare the evenness of species in two different sites?

I'm writing up some ecological fieldwork and I have presence/absence data for 50 species in 30 quadrats (samples) for each site. A few species were found in most of the samples (say 28 or 29) while ...
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92 views

Does Spearman's Rank Correlation Imply Periodicity?

I have collected data from an online survey that asked people to 'rate' a corpus of music track excerpts with 8 emotional adjectives such as 'happy', 'sad', 'angry', etc. They could only select one ...
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245 views

Examples of Non-Linear Time Series?

Does anyone have an example of real world (ideally multivariate) time-series data that depends on its past in a non-linear, but additive way? I understand that there are several examples of ...
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1answer
24 views

Should the sample sizes be equal for non-parametric tests?

I randomized samples into two experiments and I ended up with about 190 samples in one group and 80 in the other. The distributions of the two samples are not normal and I want to use Wilcoxon test to ...
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2answers
59 views

Understanding Big/Little $O_p$/$o_p$ Notation for Estimators

I am reading a Text about Single Index Models (SIM), where a SIM is defined as $E[Y|X=x] = G(X' \beta)$, with $G$ and $\beta$ unknown. After proposing an estimator for the function $G$, the ...
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37 views

Transformation of variables to fulfill normality assumption before GAM

We are running a GAM with highly skewed (and positive data) both in the dependent and in the independent variables. We have chosen to transform both the dependent variable (cubic root transformation) ...
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1answer
31 views

Test that a sample is non-randomly drawn from a population with arbitrary distribution

I have a dataset in which there are about 500 measurements for a particular scoring metric. The data are normalized so that the mean is 0 and the standard deviation is 1, but the distribution is ...
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1answer
72 views

KS Test and Wilcoxon Rank Sum Test, large differences in p values

I am relatively new to non-parametric tests. I wrote the following R code to test 2 sample tests using the KS test and the Wilcoxon Rank Sum test. Drawing 2 samples of various sizes from unit Normal ...
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28 views

How to apply non-parametric methods to panel data? “The Elite Illusion: Achievment Effects at Boston and New York Exam Schools”

I'm studying this paper The Elite Illusion: Achievment Effects at Boston and New York Exam Schools. There the authors use a fuzzy regression discontinuity design experiment to assess the ATE of going ...
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47 views

Which statistical test to use on mean data?

I have sets of data from two sample A and B. the data in sample A and B are the average mean of the population sample. Examle, sample A has list of data. each data in he sample is a an average value ...
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37 views

Skewed data, unequal n - advice?

This is the first time I have dealt with non-normal data (lucky me!), and I have come to a bit of a road block as to what tests to run. Experiment: Investigate whether false feedback affects ...
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22 views

German tank variant: estimate resolution of camera given cropped photo sizes

Make whatever assumptions you like, but I like the flavor of nonparametric techniques. I have a list of the $x_i$ by $y_i$ resolutions of a number of photos, all cropped from photos taken at the same ...
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81 views

Using KS test to evaluate differences

There are two different empirical CDFs which I have and I would like to evaluate how different they are. The place at which I started was Kolmogorov-Smirnov test - the result in my case looks like ...
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2answers
108 views

Looking for a robust, distribution-free/nonparametric distance between multivariate samples

There are many distance functions for distributions out there, but I'm having a hard time wading through them all to find one that is "distribution-free", or "nonparametric", by which I mean only ...
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40 views

How can I find out the needed sample size

I'm going to study if medical reconciliation diminishes the amount of inappropriate medications amongst elderly people in a small part of Sweden. I will count the number of inappropriate medications ...