Questions tagged [shapiro-wilk-test]

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If the assumptions of ANOVA fail to reject at 99%, how can that be applied?

I think I am on the right track, but I would rather know. Initially, when the results of Levene's and Shapiro's were significant at 95%, I tested and investigated the data in various ways. I used ...
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Confused about testing my data for normality

I am starting some quantitative analysis of a dataset. My sample size is just over 100 (approx 110) and before doing the descriptive stats I attempted some normality testing to determine if I should ...
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1answer
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Testing the Central Limit Theorem with the Shapiro-Wilk test on dice rolling simulations

Rolling a single dice repeatedly will result in a uniform distribution. But if we roll multiple dice the sum would be the Normal distribution due the Central Limit Theorem (CLT). To verify this, ...
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1answer
48 views

Shapiro -Wilk assumptions

I am doing statistical analysis in a df and I am trying to check the normality of the data. I did the Shapiro Wilk test. I think I have to check if the data meets some assumptions, this is the case in ...
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7 views

Intraclass correlation with skewed dataset

There is data on 20 people taking the same test 5 times each to look at the repeatability of the test. I understand that intraclass correlation is usually the best test to use to look at a question ...
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Shapiro-Wilks test for non-normality [duplicate]

I am using the Shapiro-Wilks test to test for normality in my data. The problem is it seems to be giving me results indicating non-normality even though some of my data is clearly normal. The p-...
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22 views

Does the effect size of a normality test determine whether the normality assumption can be ignored for parametric tests with large samples?

Reading this question and this question and the answers and comments, I have another question. Does the effect size of a normality test determine whether the normality assumption can be ignored for ...
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1answer
114 views

How to test if data follows a half-normal distribution?

There are many ways to test if the data comes from normal distribution. like this post But the question is how to test if the data follows half-normal distribution? I know Ks-test, but as the post ...
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Shapiro–Wilk normality test

I'm trying to check for normality using Shapiro–Wilk normality test. I have a two-way ANOVA (2x3) and would like to run this test on each of the 6 groups. Which function should I use to be able to run ...
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1answer
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Can we use the R square of the q-q plot as the Shapiro Wilk effect size?

The q-q plot is a nice way to see a deviation from the normality. But this is only "eye estimation" Can the R square of the linear regression be the effect size of the deviation from the ...
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1answer
33 views

Data didn't pass normality testing for K-W and S-W but the skew and kurtosis were within range...advice please?

I am conducting a study on the relationship between rural/urban living, intentions and barriers to help seeking in adult males. I was planning to conduct a correlation and then pending that result, a ...
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Three different dep. variables are significant on the Shapiro-Wilk test. That's not good. Is there anything I can do to show normality assumption?

My DVs (Facefactor, Legfactor, UpperBodyFactor) are showing sig. results on Shapiro-Wilk, meaning they are not normally distributed. The histograms look rather normal however. Is there any way to show ...
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3answers
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Quantitatively, how powerful is Shapiro-Wilk or other distribution-fit tests for small sample sizes?

I'm looking for an analysis (I assume a book or website, but feel free to put it all in comments here) that provides an in-depth discussion of the power/accuracy of normality assessments such as ...
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shapiro wilk for testing normality in ANOVA [duplicate]

This questions might be simple to most of you but while reading about Shapiro Wilk test to test the normality assumption for one-way ANOVA, I got confused. Can somebody tell me which is the correct ...
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61 views

Discrete value - Normal distribution [duplicate]

I have a data with discrete values and need to find if it is normally distributed. I plotted the graph and it looks normal and then I performed shapiro wilk test where the result were W = 0.78773, p-...
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1answer
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Shapiro-Wilk test on transformed data

I used RStudio to perform Shapiro-Wilk test for normality. In the following data set calling it $D$, I have performed Shapiro-Wilk test for normality with p-value=0.7698. 34.681 26.291 33.280 36.169 ...
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Different result from shapiro test for seemingly similar residual distributions of gls models

I have a question regarding the distribution of residuals in a gls model. I built a gls model with a numerical dependent variable (Y), a Factor A (categorical, 2 levels) and a Factor B (categorical, 3 ...
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24 views

p-value for Shapiro-Wilk is high but data doesn't appear normal

I'm a beginner at stats and I'm trying to understand p-values for paired t-test and Shapiro-Wilks using the JASP Moon and Aggression data set (hope the screenshot resolution is ok - click on the image ...
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1answer
50 views

What test is appropriate for normality?

I would like to check the normality of nearly 400 individuals. I tried many test like Shapiro test, etc...but, not much expected results. So, Could you please tell me what is the appropriate test for ...
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Why is the Shapiro-Wilk $W$ statistic defined the way it is?

In the original paper (section 2.2.), we can see that derivation of the $W$ statistic goes along these lines: Let let $m_i$ be the expected value of the $i$-th order statistic of a random sample of $...
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2answers
1k views

Limitations of Shapiro test

Are there any possible limitations to the Shapiro test or the shapiro.test() function? After removing outliers in a data set it seem that using the ...
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1answer
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Compare Z-scores (weight) before / after with a T-test?

I'd like to ask you if it's possible to perform a T test to calculate Z-scores ( weight of persons ) https://www.cdc.gov/growthcharts/clinical_charts.htm with a t test in the same group ( paired t ...
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1answer
33 views

Reasoning for tranforming linear model to log-level

I have a multiple linear regression model and found that my error terms are not normally distributed. When looking at the histogram of the dependent variable, it looks like below. I am not sure how ...
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1answer
72 views

Understanding the Shapiro-Wilk normality test

I am trying to learn how to check if the distribution of values in a set is normal or not. Making a histogram and a boxplot shows: Performing the hapiro-Wilk normality test I get: ...
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My normality plot and Shapiro's test say different things

I have an LMER, and I want to check for normality; my plots show this: However, my shapiro test shows this: ...
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245 views

Performing a shapiro-wilk test on residuals from an LMER and repeated-measures ANOVA

I would like to perform a Shapiro-Wilk test on my data which takes the form of an LMER. The LMER model is named lmerabsolute. ...
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4answers
6k views

Can a sample larger than 5,000 data points be tested for normality using shapiro.test by applying the test to a subsample?

I have a number of samples that I would like to test for normality. One of the samples exceeds 5,000 data points, the limit up to which the shapiro test accepts samples. This is the data: ...
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1answer
74 views

Alternatives to Pearson's correlation given small sample size and normality hypothesis rejected?

I would like to use Pearson's $r$ to determine the correlation strengths among around $20$ variables. Unfortunately, I had to reject the hypotheses that the data from some (around $5$) comes from ...
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1answer
47 views

Checking the normality of a large sample?

If I want to analyze a large sample size (N = 50.000) of continuous data ($ revenue) from an A/B test, what would then be the best way to check for normality? Thanks in advance!
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6answers
1k views

If a sample is not normally distributed, can a subset of the sample be normal?

I have used a Shapiro-wilk test on all of my data and the results show that it is not normally distributed. However, could this mean that a subset of my data could still be normally distributed?
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What is the difference between Shapiro-Francia and Shapiro-Wilk tests of normality?

I apologize for this easy/basic question. Please forgive me if this is a duplicate question. I've been researching the Shapiro-Wilk test (1965) of normality for a project. In doing so, I found an ...