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

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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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91 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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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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14 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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20 views

Help in handling heavily naturally skewed variables [closed]

I am doing some statistical analysis for my thesis project (not a statistics degree) and I hoped to get some help from you as the statisticians in my uni couldn't help me much. The analyses that I ...
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81 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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37 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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38 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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458 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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85 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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36 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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62 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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30 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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20 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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47 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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57 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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180 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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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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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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325 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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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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134 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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51 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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48 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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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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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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67 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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59 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 ...
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48 views

Meta-analysis of skewed data with low event rate (single-arm studies)

I am trying to pool the data from several single-arm studies regarding the re-infection rate of a certain disease using STATA. From each study, I have obtained the no. of re-infections, and the ...
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Forecasting Skew & Kurtosis

I have seen several models for estimating the expected value and variance of a distribution. I am curious, to learn if anyone has looked at models that extend beyond these first two moments ...
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Does skewness predicts variance?

(with apologizes to this question). Consider two distributions $G$, $F$ both uni-modal and absolutely continuous, square integrable and satisfying: $$F<_c G$$ this means that the standardized ...
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Best method of analysis for negatively skewed longitudinal environmental data?

I have a dataset composed of a dependent variable (species percent cover) and a range of abiotic variables (salinity, temperature, pH, water movement etc). It is a longitudinal study, in which species ...
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108 views

Log form of variables and descriptive measures

Because of larger values of variables, I did a log- transformation in my dataset. Now I want to give a descriptive table regarding my variables like mean, max, min, median, skewness, kurtosis. Can I ...
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Relationship between skew and kurtosis in a sample

It is well known that $\text{excess kurtosis} \geq \text{skew}^2 - 2$, at least in a population. However, what is the relationship between skew and excess kurtosis in a finite sample? Define excess ...
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Hypothesis test for correlation between Gamma random variables

I have two Gamma random variables. I need a hypothesis test to detect a possible correlation between them.
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Departure from normality assumption in ANOVA: is kurtosis or skewness more important?

Applied linear statistical models by Kutner et al. states the following concerning departures from the normality assumption of ANOVA models: Kurtosis of the error distribution (either more or less ...
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Compare convergence of optimization methods

I need to quantify how 2 optimization methods differ in convergence. When training a neural network I get the following plots, which show an error function after each gradient update. I think the ...
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What kind of a distribution is the total spend of a potential customer?

I'm trying to figure out how to analyse the data which consists of a number of visits to a website and the total amount the visitor ends up spending there. There are obviously a lot of zeros - people ...
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Bootstrap confidence intervals

I write to you for 3 questions. I want to calculate confidence intervals on different measures of association (Pearson's correlation coefficient, Cramer's V and the Eta-square). I will make the ...
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Standard deviation to describe variation in positively skewed data?

I'm wondering how useful the standard deviation is when applied to positively skewed data? The standard deviation implies that 68% of data will lie within one standard deviation of the mean, but ...