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

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Z-Test and Normality

Does normality apply when performing a 2-proportion Z-Test? Say for example, you're taking # of student detention/student population for January, and comparing that to # of student detention/student ...
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11 views

How important is normality assumption for a two-way repeated measures ANOVA?

I want to use two-way repeatead measures ANOVA. The dependent variable is CRP levels in three different time points in five different group of patients. Each group includes 40-42 patients, so that ...
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1answer
54 views

Is an ANOVA applicable for these data?

I have a data set from 7 groups, with 20 fish in each group. Measurement of a parameter is made on 25 cells from each fish (so each observation in the data-set is completely independent, right?). ...
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1answer
36 views

Is normality important for ANOVA when N>30?

I want to use repeatead measures ANOVA with sample size approximately n=40. Normality is violated according to S-W test. After log transformation although Q-Q plots seem better, the distribution is ...
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1answer
69 views

Could one say that one dataset is distributed more normally than another?

I am trying to fit a simple linear model: experiment ~ calculated_1. From the basic model, I get residuals_1. And I know that ...
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1answer
65 views

Anderson-Darling test for normality with estimated parameters

I have a set of measurements coming from a manufacturing processes. I want to test if the measurements come from a normal distribution. If I understadn correctly, it's wrong to use K-S test or A-D ...
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1answer
50 views

Does ARIMA require normally distributed data? [duplicate]

I want forecast inflation using ARIMA model. My questions are: Does ARIMA require normally distributed input data? (Because my data—inflation—is not normal.) If ARIMA require normally ...
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1answer
14 views

KS test for normality on residuals from OLS vs. MLE

This is a conceptual issue. Suppose, one wants to test the residuals $e_t$ from the regression for normality. So, he runs the regression, obtains the estimates of error variance $\sigma^2$, and forms ...
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2answers
64 views

Do these Q-Q graphs show that the data is approximately normally distributed?

The ends of these graphs confuse me. I know most of the values fall on or near the line. But I am unsure of whether the data is indeed approximately normal. These are the two graphs. Plot 1: ...
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2answers
117 views

What to do if residuals are not normally distributed?

I was wondering what to do with the following non-normal distribution of residuals of my multiple regression. Normality test of standardized residual ...
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2answers
48 views

Can you perform an ANOVA on r-values (correlation values)?

I am doing neuroimaging research yielding what is essentially a correlational analysis wherein my output is a brain's-worth of r-values (so like 15000 voxels worth of r-values). In this particular ...
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39 views

Non normal and nonlinear data

I'm working with pilot study data (n=70) that has two continuous response variables and a number of categorical and continuous predictors. Naturally my data does not follow a normal distribution nor ...
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5 views

Robustness to deviation from normality with regularized VAR model - references

I was listening to a talk where the presenter was talking about using regularized estimation approaches in a VAR(1) model $$X_t = \Gamma X_{t-1} + \epsilon_t, \quad \epsilon_t \sim ...
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26 views

Assuming normality in RKHS

There are some authors who assume data in a Reproducing Kernel Hilbert Space is following a normal distribution. For example, in this article, the authors use this assumption to be able to derive ...
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1answer
58 views

What to do if residual plot looks good but qq-plot doesn't, after transforming the predictor and response variables?

I'm doing a multiple regression model on environmental data and am stuck on checking the assumptions. Ultimately, I need to do a model selection for the data. There are various explanatory variables ...
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1answer
185 views

A closed form formula for the normalizing constant in standard normal auto-regressive series?

Let $Z_t = c_1Z_{t-1} + c_2Z_{t-2} + ... + c_nZ_{t-n} + c\epsilon_t$ where $Z_t, \epsilon_t \sim \mathtt{N}(0,1)$ are iid variables and $Z_s \sim \mathtt{N}(0,1)$ for all $s$. Given the values of ...
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34 views

What is the best way to test normality for a very large sample size 15000? [duplicate]

Also do I need to test the normality for the categorical data? Thanks
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1answer
32 views

Multiple comparisons with normality tests

Suppose I do $1000$ normality tests, and set $\alpha = 0.05$. When testing for normality, should I correct for multiple comparisons? So if $p>\frac{0.05}{1000}$, I should keep the null hypothesis ...
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14 views

How to assess normality of a single item variable before running ANOVA in an experiment?

In my experiment, I have 3 dependent variables, each measured through a single item. I want to assess their normality before proceeding to MANOVA. These three variables failed the Shapiro-Wilk test. ...
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1answer
53 views

Difference between the two way of performing Kolmogorov-Smirnov normality test [duplicate]

There are 2 ways to perform Kolmogorov-Smirnov test in SPSS: Analyze; Nonparametric Tests; 1-Sample K-S Analyze; Descriptive Statistics; Explore; Plots; Normality plots with tests What is the ...
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16 views

What statistics (parametric or non parametric) should I use for my data?

My data consists of two groups, one group is normally distributed (200 observations) while other is non normally distributed (200 observations). I have to compare one variable between these two ...
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1answer
36 views

How to do normality test if one factor consists of 5 questions?

I have 4 independent variables and 1 dependent variable. In my questionnaire (a likert scale), each of the factors consists of 5 questions (items). How do you do the normality test in this situation? ...
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43 views

Non-normally distributed residuals for multivariate linear regression.Still a valid model?

I try to know if the independent variables are affecting the outcome of the dependent variable, but while the Shapiro-Wilk test shows residuals non-normally distributed, the autocorrelation of errors ...
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20 views

What normality test should I use for moderate sized samples? [duplicate]

I have a sample size $N=1000$. I would like to do a normality test. What test should I use? I know the Shapiro-Wilks test. This page from laerd says that the Shapiro-Wilks test is appropriate for ...
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15 views

Non normality and nonlinearity in a generalized mixed model

My thesis is about the encroachment in Arctic regions. My experiment contained 6 plots, of each type (encroached and non-encroached) on three elevations. Elevation and type are fixed factors, plot is ...
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26 views

Weather analysis | company sales

I'm writing a python code that reads in a csv file of rain in inches for a given zip code and creates a normal distribution from the data. Ultimately, I want to be able to create some score for the ...
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2answers
56 views

How to compute Shapiro-Wilk test power?

I test normality of 12 residuals that are obtained from resid(lm(...)) command via shapiro.test. Thus I know variance, mean, ...
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1answer
37 views

Do data need to be normally distributed by group or together?

I have two groups, both male soccer players divided into professional and amateur, with knee proprioception scores for each player scored from 0-50. When analysed together they are not normally ...
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112 views

Repeated measures ANOVA: what is the normality assumption?

I am confused about the normality assumption in repeated measures ANOVA. Specifically, I am wondering what kind of normality exactly should be satisfied. In reading the literature and the answers on ...
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1answer
83 views

Normality, and when to use t-test vs. Mann-Whitney U-test?

I am looking for a few rules of thumb of when to determine that my data is 'normal enough' to use a t-test vs. a Mann-Whitney U-test. From what I have read, most real world data sets are non-normal, ...
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1answer
100 views

Cohen's D: Should I use raw data, log transformed data or back transformed data?

I am a doctor and right now I am doing medical research. I have some questions about cohen's d. I try to research it on the internet but it seems there is not much answer to this question. My project ...
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1answer
68 views

Non-normality in panel data

enter image description hereI am checking for normality after my fixed effects regression. According to the K-density graphs, the distribution looks normal but when I do the S-Wilk command, residuals ...
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73 views

How to calculate mean and standard deviation of a range variable (grades) when the raw data is based on frequency categories?

Results of an exam indicate that: 13% of the class earned an A 20% earned a B 48% earned a C 10% earned a D 9% earned F's The grade C ranges from 70-79%. Assuming that the data is normally ...
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1answer
50 views

Aren't normality tests backwards?

Currently hypothesis tests for normality are setup so that the null hypothesis is that the data is normally distributed and the alternative hypothesis is that the data is not. This seems to have ...
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65 views

Residuals Diagnostics, transformation or non-linear model

I am struggling with my data (hit counts for multiple target detection trials) To start, it is heavily negatively skewed: 00000000000000000000000000000000000 ...
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1answer
73 views

Large samples and normality of residuals

Ok I understand that normality of residuals is not really a concern in large samples. But can anyone tell how large should the sample be to ignore normality. Any cut off point? I'm working with a ...
2
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1answer
28 views

Will using Mann Whitney U test, comparing the medians, give a valid inference to the populations being compared?

I am basically comparing the length and/or weight of an animal categorised by the presence or absence of a specific allele, so I have two groups. The data for length and weight do not seem to be ...
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70 views

When to use Brown-Forsythe Test?

I have been researching the differences between Welch ANOVA and Brown-Forsythe Test. I know that Welch ANOVA is used for more than two groups comparing whether there is statistically meaningful ...
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1answer
35 views

Log transformation for logistic regression

Is it necessary to log transform non-normally distributed variables to perform logistic regression? If so, when is it appropriate?
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91 views

Consequences of violating assumptions of nonlinear regression when comparing models and/or datasets

I have a question about the consequences of using non-linear regression when the data violate the assumptions of (1) homoscedasticity and (2) normal distribution. Specifically, I am wondering about ...
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38 views

not normally distibuted residuals

I have made an linear regression model using stata. I have made my model diagnostics - predict y, predict (rstudent) residuals. When I control the residuals for normality by a Q-Q plot, it is ...
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93 views

Johansen's cointegration test in small sample under non-normality

I am looking for references regarding the behaviour of Johansen's cointegration test (trace test, perhaps also eigenvalue test) in small samples with non-normal innovations. I wonder how robust the ...
3
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1answer
64 views

Is there a rule of thumb to choose a normality test?

Is there a rule which normality test a junior statistician should use in different situations. I read from Wikipedia that there are so many. And what one can do if there is a limit case such that one ...
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26 views

Shapiro-Wilk Output [duplicate]

I have data comprised into different variables (between females and males, measurements of body fat through 3 different methods) and after running a shapiro-wilk test, the output tells me parts of the ...
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0answers
19 views

Correlating aggregated values between groups

I am currently analysing data from household surveys in 27 Indian villages in 7 states, with about 30 cases in each village (807 in total). The aim is to find relationships between various factors and ...
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18 views

May I mix pvalues from ANOVA with pvalues from Kruskal-Wallis test?

I am studying one-way Analysis of Variance (ANOVA) from this book. Suppose I want to run one-way ANOVA on multiple sets of observations. For instance, I have a matrix of $n$ features and $m$ ...
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26 views

Inferences with non-normal data

I have the data of index closing values that I later will use to run some regressions. When examining the data, I find heteroscedastic residuals and that the distribution is non-normal. In fact, it ...
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3answers
545 views

“Reversed” Shapiro–Wilk

The Sharipo-Wilk test, according to wikipedia, tests the null-hypothesis ($H_0$) "The population is normally distributed". I am looking for a similar normality test with $H_0$ "The population is not ...
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1answer
149 views

non-normal residuals in ARIMA

I am trying to fit an ARIMA model and I have already evaluated a few variations which I finally selected ARIMA(1,1,3) model. The residuals seems to be uncorrelated and all the lags are significant. ...
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shape of distribution and indepencence

I have a sample of observation on which normality tests (Anderson Darling, Shapiro - Wilks, KS,...) would accept the assumption of normality. Nevertheless I know that there is a certain time - ...