# Questions tagged [shapiro-wilk-test]

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### How to compare three groups of patients if one group is normally distributed but the other two are not?

Retrospective study involving three groups of patients. Group 1 are patient's diagnosed with sepsis. Group 2 are patient's diagnosed with a localized infection. Group 3 are "healthy" ...
1 vote
87 views

### Ambiguity between Statistic Normality Test vs Visual Normality Check

I'm learning some basic EDA using the Boston housing price dataset and I want to filter out outliers in the feature columns. To do that I first wanted to understand what distribution each of my ...
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1 vote
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### My professor insists that this data is normally distributed but I cannot work out how that can be!

I have a data set on deforestation and the impact that the distance from a road has on deforestation. For the assignment, I need to assess the correlation between these two variables. In class, my ...
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437 views

### Heteroscedasticity in linear mixed effects models (lmer)

I am computing the following model in R, using lme4::lmer: m3 = lmer(e ~ (X*Y*Z) + (1|ID/R), data = data_transform) e is a continuous variable. X, Y, and Z are ...
10 views

### Wilcoxon's Signed-Rank Test in the context of 2 algorithms and 1 domain

I'm trying to understand whether my analysis for a problem is in the right direction. I have 2 algorithms (3d object detectors) that I've applied to the same dataset to obtain TP, FP and FN's for each ...
57 views

### Can I violate assumptions of normality for categorical linear regression models?

I'm using packages included in this R/rStudio tutorial to set up some linear regression models comparing a continuous dependent variable (eccentricity) to three categorical variables (year, bird ...
63 views

### About the normality question with four conditions

I am encountering difficulties in determining the normality of data and distinguishing whether the data I have collected is parametric or non-parametric. I have gathered data using a 7-point Likert ...
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415 views

### When to use Pearson's test and when to use Spearman's test?

I want to do a correlation analysis on a dataset of 28 samples. I want to correlate the age with the size of a reflex response. But I don't understand whether I should use Pearson's or Spearman's test....
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38 views

### Do I need to use a factor for the ANOVA? [closed]

The problem: A psychologist is interested in short-term working memory under (1) sleep deprivation, (2) a strong dose of caffeine, (3) following 8 hours sleep. They conduct a between subjects design. ...
73 views

### How to test for normality on paired samples between two treatments when the number of observations per treatment is unequal?

I have mice which need to poke a device to receive food across a one hour period. The device records the number of pokes and poke_time which is the duration that the mouse remained in the poke hole. ...
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611 views

### Can I assume normal distribution?

I have calculated daily price returns of Bitcoin and plotted this data in the following way: x-axis: returns in % y-axis: count I assumed the data had a normal distribution to calculate the \rm ...
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1 vote
56 views

### Can I remove a single data point if it is changing drastically a Shapiro Wilk test?

I'm conducting a hyphotesis test to compare the mean of two independent samples. To do so, I need to check normality of both samples. I have two samples of size 20. A single data point, on both ...
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### How to determine normalcy for a one group pre-test post-test? [duplicate]

My study is a retrospective one group pre-test post-test on multiple variables. Not every patient in the study had scores for all of the variables, so as long as a patient had both a pretest and a ...
1 vote
73 views

### Are there differences for the Shapiro tests in Python and R?

I am aiming to reproduce the issue (using Python) described in the answer here Is normality testing 'essentially useless'? It states that the assumption of normality is more likely to be ...
171 views

### Why does checking normality of residuals give a different result than checking bivariate normality of the two variables?

I am checking the conditions for hypothesis testing a Pearson correlation as significant or not, and also checking the residuals normality conditions for OLS. Why are the following methods giving ...
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521 views

### How to test for normal distribution with one peak in data?

I would like to test following. Suppose I have a normal distribution with mean 1.5 and sigma 0.5 on interval [0, 3]. Python code: ...
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### What is the best test two compare samples with continuous results when there is not normality

I have a sample (n=200) and I have the results of two in silico prediction tests. Results are continuous and very similar but I want to confirm this statistically. I have done shapiro test to see if ...
8k views

### Why are Shapiro-Wilk and Kolmogorov-Smirnov test compared with same sample size?

I am trying to understand when to use Shapiro-Wilk Test and/or Kolmogorov-Smirnov Test for normality. Currently, I am following this website How to Test for Normality in R (4 Methods). This paper ...
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### What is the distribution of the test statistics for Shapiro Wilk, Anderson-Darling, and Lilliefors (KS) tests for normality under null?

Have been researching tests for normality, and have some idea of how some of these tests work from Wikipedia. However, they leave out explaining the distributions of the test statistics under the null ...
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1 vote
241 views

### Which statistical test should I use if the assumptions of a 2-way ANOVA are not met?

My study design consists of two factors (one with 2 levels, the other with 6) and a continuous response variable. In order to analyze the influence of both factors on the explanatory variable I built ...
14 views

### Normality test of vector [duplicate]

I consider the next piece of code library(UsingR) data(babies) hist(babies$wt) shapiro.test(babies$wt) As you can see the data seems perfectly normally ...
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### What test is appropriate for normality of continuos data grouped in bins

I have a data set of continuous data. From 1000 observations, the resulting dataset is only 29 rows and two columns: the range (starting point) and the count. Pearson - Weldon crabs dataset range ...
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6k views

### Why is my data not normally distributed while I have an almost perfect QQ plot and histogram?

I am doing a thesis and I am stuck with my statistics on time series data. And when I run a Shapiro test, or any test, it says: ...
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51 views

### Test for gaussian mixture fit when component assignment is known?

I have a process 𝑃 generating random variables X_1, ... X_n. From each of these I've sampled a set of samples ...
1k views

### QQ plot result doesn't correspond to normality test [duplicate]

I am considering an ANOVA model for such data: ...
1 vote
2k views

### Statistical analysis - Shapiro-Wilk test?

I apologize if this question will seem odd, but I am quite new to statistical analysis. I performed coinfection experiments with a total of 12 conditions, and I have 3 measurements per condition. I ...
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1 vote
557 views

### R: Shapiro-Wilk test yields different results in descriptives and in One-Way ANOVA

I got a dataset of 60 people from a between-subject approach that I was trying to check for normality. (Since I need information about normality for ANOVA post-hoc tests.) They were split in three ...
1 vote
404 views

### Shapiro Wilk test of normality

I ran my data under JASP and the p-value for the shapiro wilk test of normality was <.001. How do I interpret this?
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### How to transform a set of negative values to obtain a normal distribution? [duplicate]

I am having quite a few problems with transforming a set of data with values between -1 and 0, as I need to normalise them. I tried to use the following formulae: [(𝑥−min(𝑥))/(max(𝑥)−min(𝑥))] AND ...
1 vote
1k views

### Is there a way to calculate peaks of a distribution mathematically?

I’m trying to find some way to mathematically calculate the number of peaks in a distribution. I know there are various tests (such as Shapiro Wilk) that assess whether a distribution is normal, but I’...
731 views

### Two-Way anova assumptions not fulfilled

My task is to determine whether two different categorical variables (residence location (city/rural) & residence size (small/medium/large)) have a connection on one numeric variable (residence ...
106 views

### if I have a variable in my data that is not normally distributed, could I still use an ANOVA if my sample size is large enough?

I have a sample size that is more than 30 but one of my continuous variables is not normally distributed. The Shapiro-Willk test does say that my data is not normally distributed. I am going to ...
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### Concept Clarification: Wilcoxon rank test vs two-samples T-test (UPDATE)

I am currently deciding whether to use the Wilcoxon rank test vs two-samples T-test to assess BMI between two unrelated groups. Using the following code to assess normality ...
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15k views

### Best statistical test to compare two groups when they have different distributions

I am teaching myself to use and apply statistics to a big database. I have 2 groups that I wish to compare, healty controls (HC) and patients (P). The sizes are HC= 84, P= 196. Each group has many ...
1 vote
176 views

### 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 ...
428 views

### 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, ...
254 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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### 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 ...
1k 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 ...
388 views

### 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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### 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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1 vote
163 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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### 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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### 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-...
1k views

### 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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### 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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### 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 ...
### 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 \$...