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

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Can I use the chi-squared test of independence with skewed data?

I have two variables, both categorical, one with skewed responses. How do you deal with skewed data in the chi-squared test? Are there any other relevant tests? I want to perform the test in SPSS.
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15 views

Model choice for nonnegative and positive continuous right skewed outcome

I am trying to analyze a set of nonnegative continuous non-integer data (i.e. the data points are not counts) that are mostly between 0 and 3 whose distribution is highly right-skewed even after log ...
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22 views

Analyzing the shape of distribution on a histogram [duplicate]

I have three different histograms which are generated from one sample. In each of the histograms, both variables are the same. Although binwidths for each histogram is different. By looking at each of ...
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17 views

Distribution heavily stacked on either limit - appropriate test?

I have two sets of results from an experiment that produces distributions with extremely heavily stacked sides and mostly uniform elsewhere. The aim of my analysis is to answer a the question roughly ...
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40 views

Visualizing many left-skewed distributions

I have a series of left-skewed/heavy tailed distributions that I would like to show. There are 42 distributions across three factors (labeled as A, ...
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42 views

Appropriate distribution for bounded data set

I am designing a points-scored test. There is a limit on the maximum amount of points possible, as well as on the fewest amount of points possible. I have had a test group take the test and graphed ...
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36 views

Statistical tests for comparing a skewed clinical sample

I recently surveyed 350 low-income families -- they were randomly split into two groups: control and treatment. One of the variables I am very interested in is the amount of savings of each family. ...
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42 views

Is skewness always bad?

In my experiment, I hypothesised that individuals in one treatment condition would give higher values on a likert scale than individuals in the other treatment condition. It was a one tailed ...
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413 views

Real life examples of distributions with negative skewness

Much along the lines of the "real-life examples of common distributions" I'm interested if anyone has any pedagogical examples used to teach negative skewness? There are plenty of canonical examples ...
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40 views

Single-pass algorithm for kurtosis

Here is a simple test I've run on MATLAB to check the validity of a single pass (online) algorithm for computing $3$rd moment and $4$th moment. ...
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94 views

extremely left-skewed response variable - how do I model this dataset?

This is a histogram showing my response variable. The response is # (or proportion? or percent?) of aphids eaten off of cards in fields, to model predation by natural enemies. Predictors: fixed ...
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50 views

Taylor expansion to contain sample mean, sample variance, sample skewness, and sample kurtosis

I have the following expression: $$\frac{1}{p} \ln\left(1+\frac{p^1}{1!n}\sum_{i=1}^n x_i + \frac{p^2}{2!n} \sum_{i=1}^n x_i^2 + \frac{p^3}{3!n} \sum_{i=1}^n x_i^3 + \frac{p^4}{4!n} \sum_{i=1}^n ...
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114 views

Transforming extremely skewed distributions

Assume that I have a variable whose distribution is skewed positively to a very high degree, such that taking the log will not be sufficient in order to bring it within the range of skewness for a ...
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15 views

Multivariate skew normal [duplicate]

In the maximum likelihood estimation of Skew Normal, how does R calculate the mean? You know the formula is \begin{equation} \mu=\frac{ \sum_{i} x_{i} W(x_{i})}{\sum_{i} W(x_{i})} \end{equation}. ...
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212 views

Calculating statistical significance with unequal sample sizes and unequal variances

I have two samples, one with $n_1 = 41,000$ and the other with $n_2 = 881$; the larger sample has a standard deviation of $13.74$, and the smaller has an $SD=10.75$. The means are different, and when ...
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57 views

Estimating parameters for univariate skew t

How can I solve the MLE for the skew-t distribution via EM? I am comfortable with the EM methods for t, so could someone show it for the skew-t?
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51 views

Parameter estimates for skew normal distribution

What are the formulaic parameter estimates for the skew-normal? If you can, the derivation via MLE or Mom would be great too. Thanks Edit. I have a set of data for which I can tell visually by plots ...
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7 views

SNEP distribution fitting and parameter estimates

I'm looking to try and fit a SNEP distrib to some data but am not sure how to go about this - can anyone give me some derivations for parameter estimates etc?
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2answers
65 views

Skewness adjusted t-stat

I've some data that is divided into a series of groups and am testing whether the mean is different from 1. The data is highly skewed, with skewness ranging from 1.10 to 26! I did a one-sample t-test ...
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Summing Transformed Variables

I am using regression, and trying to create a construct. I have two continuous variables but they are each skewed/not normally distributed. I have $\log_{10}$ transformed each of them separately. Is ...
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65 views

Do all these estimates of kurtosis and skewness have the same (asymptotic) distribution under normal sample distribution?

I have seen five types of estimates of kurtosis and skewness: three from http://stats.stackexchange.com/a/84057/1005 one from page 9 of Analysis of Financial Time Series by Ruey S. Tsay one from ...
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29 views

How to model zero-inflated continuous response using categorical predictors - preferably resulting in multiplicative parameters

I'm having trouble finding a suitable model for predicting the AVG value (revenue in cents) of a single click on a product on a large e-commerce site. (assuming a click leading directly to a purchase ...
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64 views

Consistent, non-parametric, robust (to fat tails) estimation of expected value of an asymmetric distribution

Question: Is anyone aware of a consistent, non-parametric estimator of the expected value of an asymmetric distribution that is robust to fat tails? What if we constrain ourselves to the class of ...
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36 views

Can I use Mean values of likert resposes instead of factor scores in case of skewed values?

I have five point likert scale responses ((1-most imp, 5-least imp) for 14 items that I want convert them into 5 factors with confirmatory factor analysis. I already have designed which item should go ...
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Simulate missing data for multivariate distribution?

(Following the private request from a more senior CV member, I am editing this question to make it more readable and comply with CV standards). I am looking for a method to simulate multivariate, ...
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75 views

Designing a probability function with a desired kurtosis and skewness

Is it possible to design a probability function P(x) such that the distribution will have a specified kurtosis, K, and skewness, S? I am not otherwise interested in any other properties of this ...
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72 views

graphical and statistical approach to evaluate the skewness and kurtosis of a data set

In practice, we may always be asked to check the skewness and kurtosis of a data set. I have two questions. Given a probability distribution, how can we determine/evaluate the skewness and kurtosis ...
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Why does the accuracy of the central limit theorem for a mean depends on the skewness of the random variables being summed?

The accuracy of the central limit theorem for a mean depends on the skewness of the random variables being summed. Could someone explain that to me? Or could someone propose a book to read? ...
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94 views

Mann-Whitney test on two skewed (Poisson) data sets reject H0 but confidence interval is nearly zero

I'm comparing two sets of samples, X=(x1, x2, ...) and Y=(y1, y2, ...), where xn and yn is an integer (discrete number) from 2-14 denoting the count of a certain event produced by n. The sets differ ...
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49 views

Guidelines for splitting positively-skewed DV for Linear Modeling?

I am creating a multiple Linear Regression model using a Dependent variable which is extremely positively-skewed: My skewness statistic is 27.610, std. deviation is 2832.139, range of values from 0 - ...
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67 views

Interpretaton and Implementation of the Coefficient of Skewness

Direction: Achieve the result based on the table and its data by using Coefficient of skewness (CS). Obstacle: I have difficult to make a calculation step by step based on the equation below. I need ...
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Generating skewed correlated data in R

I am interested in generating correlated, skewed data in order to evaluate the application of a statistical approach to a data set I am analyzing. Specifically, I have two correlated variables, and I ...
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t-test on highly skewed data

I have a data set with tens of thousands of observations of medical cost data. This data is highly skewed to the right and has a lot of zeros. It looks like this for two sets of people (in this case ...
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Looking for metric to measure linear and constrained relationship between 2 variables

Data are 2D x-y pairs, both of which have [0-1] possible range. I need to calculate how well these data fit a linear relationship, where the intercept is 0 and the slope is 1. In other words, a ...
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85 views

Best way to convey highly skewed data

I am estimating a linear probability model with a hierarchical structure. I am bootstrapping standard errors to test the significance of the coefficients in order to double check the parametric ...
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220 views

Logistic regression diagnostics when predictors all have skewed distributions

I'm fitting a logistic regression model Y ~ X1...X10 to 10,000 observations, where my goal is estimate the effect of each covariate on Y. My first issue is deciding what transformations to apply to ...
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How to prepare variables with mild skew for multiple regression?

I am doing some univariate analysis on a variable before doing regression. I think it is very skewed. Three histograms are of (1) the original variable; (2) log10 transformation, and (3) inverse of ...
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170 views

Count data as an independent variable in OLS- using a dummy variable+ the variable linearly to account for skewness

I am using OLS to model the relationship between amount of foreign aid (dependent variable, logged) and media coverage (number of newspaper articles, count variable). I assume a linear relationship ...
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What does “s” represent in the formula for skewness?

I need to use a test for normality for a problem. By calculating skewness, there is a formula, which is: $$ \text{skewness} = \frac{\sum (x_i -\bar{x})^3/n}{s^3} $$ where $\bar{x}$ is the sample ...
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Two-sample location test when data is heavily skewed towards zero?

I want to test if the mean between two independent samples is different. Both samples are large, about 2 million observations each, however almost all of the observations are zero. In particular in ...
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23 views

How to improve location and scatter estimation conditioning on higher order statistics?

Using sample moments, how can the mean and variance estimators be improved if e.g. skewness and kurtosis are known exactly? And what about using estimates for these instead, which should imho be of no ...
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130 views

Proper regression model for ratio data

I've been thinking about a regression model with dependent variable a ratio in the range [0-600+]. About 50%+ are 0 values though, 40%+ values [0-5], and a very small percentage of the values are ...
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90 views

Consecutive Log Transformations

I have a dataset where I am trying to enforce normality on positively-skewed variables. I've found that consecutive log transformations help in achieving normality but am wondering if there is any ...
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111 views

Cronbach's Alpha and Skewed Data

I am attempting to assess the internal reliability of a questionnaire, but the results are highly negatively skewed. Range = 6-20 Median = 20 IQR* = 1 Log normalisation doesn't work. Is there an ...
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470 views

Method for generating correlated non-normal data

I'm interested in finding out a method for generating correlated, non-normal data. So ideally some sort of distribution that takes in a covariance (or correlation) matrix as a parameter and generates ...
2
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1answer
135 views

Sample size for a very skewed A/B Test

I would like to perform an A/B Test on my website. I have basic knowledge on know how to do a basic test statistics, but I'm not sure on how to choose the sample size. In particular, if I have an ...
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419 views

Skewed but bell-shaped still considered as normal distribution for ANOVA?

This could be a pretty basic question, I'm a little rusty on my stats knowledge. Background: I am monitoring website load time performance. To do so, I have a script running and capturing data ...
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140 views

Transforming data with both negative and positive skew

I am attempting to run a MANCOVA of memory assessment data. My IV has three levels (no memory impairment, moderate memory impairment, and severe memory impairment). The covariate is education. The DV ...
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119 views

Skewness in residuals

I have skewness of -0.5 in the residuals which does not seem to be improve much after using logs/root. Is this a major concern? Tests relating to homoskedasticity, multicollinearity, outliers all ...
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337 views

Log-linear transformation

I have transformed my variables using the ln function in Stata in order to solve some issues relating to the assumptions of the linear regression model. Whilst most ...