Skewness measures (or refers to) a degree of asymmetry in the distribution of a variable.

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Estimating medians and modes of skewed distributions using GLMs

Edited question (less vague hopefully) I am wondering why for generalized linear models with Gamma, Poisson and Negative Binomial distributions that there appears to be no discussion about estimating ...
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measure of multivariate skewness

I am looking for a generalization of Pearson's or the Yule-Kendall's skewness measures, from univariate to multivariate data. If not a proper generalization, any other measure sensitive to the ...
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Is it possible for a random variable with 0 mean to have a positive expectation after compounding many observations?

Basic example, assume that the expected daily return of the S&P 500 stock market index is 0, i.e., the return on any given day of the stock market is 0.0%. But, we also (generally) expect that ...
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How to analyse skewed and unskewed data on SPSS?

Study design: I have shown participants a series of photos of themselves vs. other people's bodies (original and manipulated), and asked them to find the original. Their responses were recorded and ...
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20 views

How to scale a skewed-distribution predictor for a neural network?

I’d like to ask what would be the more appropriate way of introducing a predictor variable with a highly skewed distribution into a neural network model. Suppose I had a variable whose distribution ...
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51 views

Creating a probability distribution that is truncated skewed

I have a dataset I want to use to generate a probability distribution. The distribution is skewed and can only include positive integers. I've tried normal (both skewed and truncated, although I ...
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50 views

Testing for normality in non-normal distributions with zero skewness and zero excess kurtosis

[This question was formerly called "On Non-normal distributions with zero skewness and zero excess kurtosis" and relabeled to better reflect its focus.] I am trying to write a little simulation using ...
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33 views

How to analyze skewed and unskewed data on SPSS?

Study design: I have shown participants a series of photos of themselves vs. other people's bodies (original and manipulated), and asked them to find the original. Their responses were recorded and ...
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0answers
6 views

Skewness and metrics for selection

Considering results of an experiment of examining 2 different methods against 152 samples, grouped in 8 groups. Also assuming that we acquired the skewness value for each group. If we are willing to ...
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42 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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44 views

Comparing several asymmetric distributions

I have constructed 3 toy distributions using R ...
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33 views

click through rate stats

I have a group of 10 users. Each user receives a daily notification for one week. Ideally, each user will click on all notifications received. At the end of the week I collect the number of clicks per ...
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20 views

Down-sampled training set with unbalanced test set

Data: https://www.kaggle.com/c/GiveMeSomeCredit/data (cs-training.csv) Training Tool: Python, Numpy, Pandas Balancing data with down sampling is a recommended solution to data imbalance. I balanced ...
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29 views

Help with highly skewed data

I have a response variable which is highly skewed and has a high percentage of zeros. I am looking for some guidance around what modeling technique to use and the process to follow. As an ...
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106 views

Transform normal distribution to skewed distribution without changing its support

I've found many questions and answers about transforming skewed distribution to normal. This question might arise because the simplicity of working with normal data. But, is there any function that ...
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20 views

Comparing two data sets for a trend in the data

I have two data sets ( have only access to the statistics of data sets like mean, percentile, count etc but not the data it self). I am interested if I could have a metric which can answer below ...
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22 views

inequality measures for comparing two distributions

I have asked this question in stack-overflow [link] and someone suggested that this might be a better place for my question: I am looking for an inequality measure to compare the inequality between ...
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95 views

Taming of the skew… Why are there so many skew functions?

I am hoping to have more insight on the four types of skew from this community. The types I refer to are mentioned in the http://www.inside-r.org/packages/cran/e1071/docs/skewness help page. The old ...
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Where does SKEW Excel equation come from?

I need to quote Excel's skew equation in a paper but I couldn't find any information about this equation: $n$: size of the population $s$: standard deviation signed $x$: mean Does anyone know ...
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48 views

Find the values between percentiles in a frequency distribution

In the distribution below, how would I find the values that lies between 30% and 50% of the distribution? R code would be handy but not essential! 28, 28, 29, 30, 30, 31, 31, 31, 31, 32, 32, 32, 34, ...
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Unbiased estimators of skewness and kurtosis

The skewness and kurtosis are defined as: $$\zeta_3 = \frac{E[(X-\mu)^3]}{E[(X-\mu)^2]^{3/2}} = \frac{\mu_3}{\sigma^3}$$ $$\zeta_4 = \frac{E[(X-\mu)^4]}{E[(X-\mu)^2]^2} = \frac{\mu_4}{\sigma^4}$$ The ...
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measure development - removing items from an item pool due to ceiling effect

During the early stages of scale development, many items within our item pool were found to have a strong ceiling effect with low score variability. In order to attempt create a meaningful measure ...
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63 views

Difference between skewness formulas

I recently started learning statistics. I got problem while learning skewness & kurtosis concept i.e in my search for formulas regarding skewness & kurtosis it is showing two different ...
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482 views

Is a fat tail same as skew

I keep hearing these terms, and it seems like both refer to the same thing: a greater probability of an event occurring at the extreme values of a distribution, far away from the mean (more than 3 ...
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skewness and kurtosis - different definitions

The goal of my project in Maple is to compare different theories about skewness and kurtosis. I found in literature different definitions of both. How can I compare them? Unfortunately I don't have ...
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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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132 views

Looking for a distribution where: Mean=0, variance is variable, Skew=0 and kurtosis is variable

I am aiming to run simulations in order to estimate the influence of the distribution of $Y$ (independent variable) on a certain binary outcome $X$ (dependent variable). $Y$ must always has a mean of ...
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42 views

Calculate Significance between samples with skewed data

Background: I have a sample that is very left skewed. The mean of this sample is 4.01 (min = 1, max = 5). I would like to know whether or not a subset of this sample is significantly different than ...
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121 views

Simulate non-normal data for multiple regression

In a working paper, Luo (2011) analyzes generating non-normal data, using Fleishman power method. But this approach just can be used for specific skewness and kurtosis. I would like to simulate ...
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38 views

simulation of endogenous skewed regressor

I have a question regarding endogeneity. I have to simulate a variable that is skewed and at the same time correlated with the error term, whereas the error term, as well as two other exogenous ...
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21 views

interpret normal probability plot of residuals [duplicate]

I am looking at two normal probability plots of some residuals from a two different regressions. I am trying to make sure I fully understand what they are telling me. The first chart below appears ...
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How can I write a skew-normal distribution function given these 3 points?

Suppose I have a set of normally distributed data with mean µ, such that 34% of the data lie between µ–σ and µ, and 34% more of the data lie between µ and µ+σ. Then we know I can write a distribution ...
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96 views

Fitting an asymmetric Gaussian

I've got some spectral data that I'm processing, but there is a clear skew in the data. What I need is to quantify how asymmetric the data is, and to plot a skewed Gaussian in order to obtain the ...
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94 views

Error bars on graph, skewed data, negative standard deviation

I have only had basic stats. I conducted some research where I have four different treatments and results for the data range from 0-6. I don't need any elaborate stats test, I just want to know how I ...
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195 views

Comparing and visualising highly skewed distributions

The data I'm working with are highly skewed, with the vast majority of data concentrated at 0. It seems really hard to highlight the differences between these kind of distributions: ...
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a perfect or symmetric bimodal distribution

I would like to know how I can measure the degree of symmetry of a bimodal distribution. Is there any a criterion like for example skewness in the case of unimodal distributions?
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Skewed response variable LM [duplicate]

I have a positive asymmetric response variable in a regression model. One of the assumptions about linear model is that the stochastic component of the model is normally distributed. If I have a ...
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49 views

Why is kurtosis of a normal distribution = 3 and skewness = 0, Mathematically

Now I understand that kurtosis = 4th moment / Std ^4 ... where the 4th moment = 3*std^4. so eventually k = 3. But for the report I am working on, my prof needs me to prove it using guassian PDF. can ...
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Measurement that the model is good enough for prediction

I hope can help me with this general question, First of all my dependent variable in the number of patents per year per firm (its a case study about 3 large pharmaceuticals). So after consulting in ...
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117 views

Fit very Skewed Data with Large Amount of Zeros in GLM in R

Problem I was hoping someone could help me fit an unusual data set which includes a large amount of 0's in my dependent variable in R. Model My goal is to find which variables (tyre brand ...
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1answer
568 views

how to determine skewness from histogram with outliers?

I have the following histogram created in Minitab. I am wondering whether this histogram is actually positively skewed, negatively skewed, or symmetric. By observing the graph itself, it seems that ...
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30 views

imbalance in sample size at multilevel longitudinal data

I have longitudinal data (BMI level) measured at 3 time points and subjects are students nested to schools. The sample size in school level differs considerably (n=85 % in school 1, n=10 % in school ...
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1answer
161 views

Incorrect Kurtosis, Skewness and coefficient Bimodality values?

This is my first post in CrossValidated and hope you can solve my problem. I've tried to calculate the bimodality coefficient (b) of two frequency distributions by using this formula: where g is de ...
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52 views

Disproportioned contingency table

I have a database of clients, some of which have gotten a special pill - and the rest have not gotten the special pill. Afterwards I measure if the clients starts exercising. My contingency table ...
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Transformations for a [0,1] covariate in polynomial regression

I have a polynomial regression in the form of $y = a + b_1x_1 + b_2x_1^2 + b_3x_2 + ...$ I am interested in the interpretation of the regression coefficients, specifically if the relationship of $y$ ...
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55 views

Transforming Negatively Skewed Independent Groups

I have two independent groups, (roughly 30 in each) – and their performance on 3 different tasks, there are 10 scores in total for each group. The majority of them are negatively skewed so I know I ...
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80 views

Whitening transformation for skewness?

Let $X$ be an $(m,n)$-matrix interpreted as a two dimensional array with each column representing $m$ samples from a random variable, with known covariance matrx $M$ and mean equal to $0$, it is ...
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39 views

Regression with negative skewed data [duplicate]

Sorry I was told that my question previously didn't contain enough detail so I'm trying to reword. I have a large dataset (circa 700 obs) consisting of a continuous response variable and a series of ...
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76 views

How to calculate skewness and kurtosis in parallel?

I wanted to know is there any way to calculate skewness and kurtosis of a set as a combination of skewness and kurtosis of its subsets ? So, For example if my data is, ...
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69 views

Transform sample to achieve target mean, skewness, etc

I have a sample of data with N values from which I calculate basic moments such as mean, standard deviation and skewness. I will then change these moments to different values according to my own ...