Questions tagged [shapiro-wilk-test]
The shapiro-wilk-test tag has no usage guidance.
59
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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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3
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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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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. ...
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2
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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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2
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Can I assume normal distribution?
I have calculated daily price returns of Bitcoin and plotted this data in the following way:
x-axis: count
y-axis: returns in %
I assumed the data had a normal distribution to calculate the
$$\rm ...
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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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20
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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 ...
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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 ...
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1
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131
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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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Bayesian alternatives of statistical tests [duplicate]
Are there Bayesian alternatives of common statistical tests - Shapiro–Wilk test, Student's t-test, Welch's t-test etc?
Bayesian - I mean without P-values.
References to statistical literature are ...
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461
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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 ...
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Do I need to transform data that is in these units (percentage, degrees, kg/cm or meters) before performing a shapiro wilks test for normality?
I have a few variables in these units that I would like to do a two sample t test on. I don't know if I need to transform the data first or if I can check the normalization with the shapiro wilks test ...
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2
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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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1
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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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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 ...
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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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119
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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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4
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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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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 ...
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2
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804
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QQ plot result doesn't correspond to normality test [duplicate]
I am considering an ANOVA model for such data:
...
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1
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1k
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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
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407
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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 ...
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306
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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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527
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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
...
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0
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846
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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’...
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530
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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 ...
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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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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 ...
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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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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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1
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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 ...
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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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357
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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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1
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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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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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3
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428
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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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299
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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-...
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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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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 ...
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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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2
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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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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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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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1
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1k
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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 a Shapiro-Wilk test say different things
I have an LMER, and I want to check for normality; my plots show this:
However, my Shapiro-Wilk test shows this:
...
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