Refers to the normal distribution, the Gaussian continuous probability distribution.

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1answer
42 views

Meaning of Qqnorm plot in R

I am testing the normality of a sample with R using qqnorm. I obtain this: I understand that the meaning of this plot is that the sample has fat tails. But what is the meaning of the values on the ...
0
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1answer
27 views

Kalman filter and Box-Cox

I'm interested in wind forecasting, which I have analyzed over some time by means of ARMA methods. Now I've being reading about Kalman filtering. Kalman filter is optimal when Gaussian assumption can ...
0
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1answer
19 views

Finding the probability of normality via Anderson-Darling, Shapiro-Wilk , and Kolomogrov-Smirov

I have quite a few distributions that were generated by some system, and I am trying to find the probability of accordance to normality for these distributions. So, the probability of accordance to ...
1
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1answer
42 views

how do normality check in ks test assess for equivalence or difference in data sets?

I have a series of data of photon counts versus time. These data are periodic, then I can fold them and obtain an average profile of the data. Nonetheless, some variations appear sometime in the ...
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0answers
13 views

SEM for Non-Normal Ordinal Data

In short, I conducted a satisfaction survey in which surveyees are required to answer on a satisfaction scale from 1 to 7: 285 observations, 37 satisfaction variables. Here is an example of what the ...
1
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1answer
16 views

Similarity Coefficient and Geochemical Correlation

I have a set of around 160 samples from different sediment bodies, or stratigraphic units, which I am attempting to correlate using geochemical analysis of 25 elements for each sample, and a ...
4
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1answer
238 views

Testing large dataset for normality - how and is it reliable?

I'm examining a part of my dataset containing 46840 double values ranging from 1 to 1690 grouped in two groups. In order to analyze the differences between these groups I started by examining the ...
3
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1answer
36 views

Using Univariate ANOVA with non-normally distributed data

If my data are non-normally distributed and I'm conducting a 2x2 ANOVA, what can I do to correct for this problem so I can report the main effect and interaction output appropriately? Only one ...
1
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1answer
14 views

Use pc scores to check mulitvariate normality

How can you check multivariate normality, using the scores from the PCA? Or what can we expect about the scores if the data is multivariate normal distributed?
3
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2answers
45 views

How much is moderate violation to normality for one sample t-test?

I want to test if my data have a mean equal to zero (Ho: mu=0). The sample size in not large (n=21). My variable is numerical with average -0.10 and sample_sd 0.05. I don't know the population ...
1
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1answer
65 views

Why is Shapiro–Wilk test considered to be the best normality test?

I have read somewhere in the literature that the Shapiro–Wilk test is considered to be the best normality test because for a given significance level, $\alpha$, the probability of rejecting the null ...
0
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1answer
25 views

ANOVA normality assumption for which variables?

When I want to conduct a repeated measures ANOVA pre and post test scores, which variables need to be tested for normality? Each the pre and post scores or the difference between them? I suppose ...
0
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0answers
28 views

Can I normalize a data proportion?

Is there any way to normalize this variable (attached)? In fact, this is a proportional data (a percentage). But I need transform it in order to do some contrasts. I try with arcsine transformation: 2 ...
2
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2answers
124 views

Standard error of regression coefficients without an assumption of homoscedastic normal noise

I have a time series that is affected by two (or more) kinds of events. When event $A$ happens, some signal is linearly added to the time series (the signal lasts, for example, for 100 time points). ...
0
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0answers
28 views

Determining the number of levels in a Repeated Measures ANOVA for multivariate or univariate within subjects effects

Maxwell and Delaney (1990) wrote that the multivariate approach should not be used for a repeated measures ANOVA for within subjects effects if n is less than "a + 10" (a is the number of levels for ...
1
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1answer
36 views

Total scores are normally distributed, but subtest scores are not; what to do?

I have two sets of data for males and females: $n=33$. I'd like to compare test results for both groups. I want to do a $t$ test, and I know my data should be normally distributed if I want to use a ...
2
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1answer
65 views

transformation to normality of the dependent variable in multiple regression

Is it really important to normalize dependent variables in multiple regression or are there any exceptions? My model is providing better results with more significant hypothesis when the DVs are not ...
0
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0answers
29 views

How to interpret probability plot?

I was reading about how to find the distribution of data from this question I generated the following probability plot from the scipy package.scipy prob plot Can someone please help me figure out ...
0
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0answers
20 views

Regarding transformation of a variable to follow normality [duplicate]

When I plotted histogram of a variable to see whether it follows normality, I got a highly positive skewed graph, more like that of a Poisson/exponential distribution. Now, what kind of ...
1
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1answer
66 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 ...
4
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1answer
64 views

Non-normal residuals - P-values higher or lower?

Background: I have estimated a model using panel data with the Arellano Bond estimator (see e.g., http://www.fordham.edu/economics/mcleod/Elitz-usingArellano%E2%80%93BondGMMEstimators.pdf) and n=300. ...
0
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0answers
58 views

Why do some researchers test for normality of sample data?

I once was a research assistant for a professor who wanted me to do some regressions, but before that he wanted me to test all the sample data for the variables to ensure they were normally ...
3
votes
1answer
398 views

Jarque-Bera normality test in R

Jarque-Bera normality test has significant p-values even when there is skewness and kurtosis. Does that mean test is infering data distribution is approximately normal?
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1answer
35 views

should both scores of 2 time points be of same scale in mixed ANOVA

I am running mixed ANOVA as repeated measurement analysis for cognitive score at 2 time points for 2 groups (blood pressure low vs. High). The the score at time 1 was normally distributed and at time ...
3
votes
3answers
124 views

Can a normal approximation assumption justify itself?

I am learning elementary statistics. I found an exercise, which asks to compute the desired sample size for some interval for standard error. The solution, in class slides, first assumes the sample ...
1
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1answer
22 views

Repeat normality check after modifying group cut-off?

I have a set of data which consists of one independent variable (2 groups) and one dependent variable. I successfully checked for normality (each group separately) and conducted a t-test. Now I want ...
1
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0answers
58 views

Proof that the log-likelihood is asymptotically quadratic

I was reading this article, where the author says that Maximum Likelihood (ML) estimates are asymptotically normal if the log-likelihood is asymptotically quadratic. I have heard or read other ...
0
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1answer
79 views

How to calculate power of different normality tests such as Shapiro-Wilk, Ryan test etc [closed]

Normality test for small samples with power comparison
2
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1answer
82 views

Does a Gaussian mixture model always imply a within-class multivariate normal probability distribution?

If I use a latent profile analysis (Gaussian Mixture Model) to model my observed multivariate probability distribution as a mixture (K-classes) of conditionally-independent normal pdfs, does this ...
0
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0answers
28 views

Derivation for the area formula for a sample data taken from a population that is normally distributed?

I need to understand where this formula comes from and what starting assumptions are required to get there: $ f_i = \frac{i-0.375}{n+0.25}$ where $i$ is the index (the position of the data value in ...
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2answers
69 views

Two-way ANOVA on not completely normal residuals

I have 2 factors, one (Page type) of 2 levels and the other (Intensity) of 4 levels. I did a 2x4 Full Factorial Design with 10 replications, so I did 80 experiments. Then I wanted to do a two-way ...
2
votes
3answers
197 views

Does ARIMA require normally distributed errors or normally distributed input data?

I have two questions related to time series forecasting with ARIMA: Does ARIMA require normally distributed errors or normally distributed input data ? Are there any assumptions on input time series ...
4
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1answer
153 views

Small sample sizes and the Kolmogorov-Smirnov test

I have split my data set into four categories but one of them only has four data points in it. I have run K-S normality tests on the other three categories which are each normal and when the data ...
0
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1answer
22 views

should the sample be homogenous for developing a tool supposed to be generalized across 4 countries??

I am planning to develop a new tool and planning to use it across 4 countries. For the tool validation, is it right to include sample from very large population of 4 countries? Will it affect the ...
1
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1answer
65 views

Visually inspecting normality of variables

I'm using R to plot some graphs for visually inspecting the normality of variables that will go into a linear regression model. Except for a histogram and a QQ plot, what other graphics could I use?
0
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80 views

How to compare differences in the mean when the data isn't normal

I have two sets of mean data that I have done a Kolmogorov-Smirnov test on. The tests came back showing that one data set was normal, but the other was not. The two data sets are independent of each ...
2
votes
1answer
157 views

Non-normality of residuals in linear regression of very large sample in SPSS

I have a dataset of ~17,000 cases in SPSS 21 with which I am trying to run multiple linear regression. I have plotted the Studentised residuals against the unstandardised predicted values and also ...
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0answers
60 views

Testing to see if a population is normal?

I'm an amateur statistician. I do it mostly for fun. I'm finishing up on my first semester stats class that covers up to hypothesis testing. I'm planning on beginning learning simple regression ...
2
votes
2answers
166 views

Panel data: OLS assumptions

I am trying to run an econometric panel data (fixed effects) model with about 4000 observations (so not a small dataset). My data consists of transactions (buy and sell). The transactions are linked ...
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0answers
140 views

Diagnosis of normality assumption and fitting linear regression in R

I am using the data veteran from R package survival. How can I diagnose the normality ...
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0answers
55 views

Transformation to normality for random variables with different locations

I have a (potentially infinite) sequence of random variables $X_i$, with $i = 1, 2, \dots$, which have the same distribution (in terms of "shape"), but different locations. I have a sample of size ...
0
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0answers
75 views

MANOVA multivariate normality

I'm running some analysis of student data and I'm having some questions regarding multivariate normality assumption of MANOVA. Should it be done using values of dependent variables or their residuals? ...
1
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1answer
32 views

how to test most frequent variable between groups?

I have different groups of dolphins, some with offspring, some without. I'll count how many types of vocalizations were emitted by each group, and want to find out if there is a statistical difference ...
9
votes
3answers
357 views

Assessing the power of a normality test (in R)

I want to assess the accuracy of normality tests over different sample sizes in R (I realize that normality tests may be misleading). For example, to look at the Shapiro-Wilk test, I'm conducting the ...
0
votes
3answers
427 views

Paired t-test for binary data

I have one sample with n=170 and two binary variables (A,B) that can take as a value 1 or 0, where 1 counts as a success and 0 counts as a failure. What I want to know is whether the means of these ...
2
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0answers
44 views

Comparison of cell counts with a right censoring

I have cell counts related to the action of different microorganisms and I want to compare their distribution. It's supposed they follow a normal distribution after a log transformation, but I can't ...
5
votes
2answers
253 views

Normality Testing - Choose the transformation that makes the data “most normal”?

Background: I have conducted some testing on a random sample of n=20 parts. The data is variable and I know nothing about the population statistics. I would like to use the data from this sample to ...
4
votes
1answer
250 views

Whether to test items for normality (and transform) when performing confirmatory factor analysis on a set of scales?

I received the following email: My project involves rewording a questionnaire and seeing if the internal reliability and CFA results improve. There are 30 items that are meant to form 4 subscales. ...
2
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0answers
207 views

Violation of Normality in Mixed Design ANOVA

I conducted a study in which two groups of teachers (pre-service and veteran) all watched four video clips of instances of aggression between students. The clips differed by type of aggression and ...
2
votes
1answer
149 views

How to estimate a standardized mean difference from two samples' quartiles?

I'd appreciate ideas about how to estimate the standardized mean difference (SMD) for two independent samples from each sample's size and middle three quartiles (i.e., median and 25th and 75th ...