242 questions linked to/from Is normality testing 'essentially useless'?
508 views

### Fitting data to a log-normal distribution [duplicate]

For a simulation study I've been trying to find an appropriate distribution for job handling times in R. I have a very large dataset of 77010 records (handling time in seconds). I've been exploring ...
380 views

### Normality test and Outlier detection [duplicate]

In this question, I would like to ask two things: outlier detection normality test Details are as follows: I need to detect and remove outliers in my data. Before doing that, I want to test if my ...
185 views

### Is the practice of doing normality test before doing t test wrong? [duplicate]

When I read research papers, I saw that many people do a normality test first, then decide if a t-test or a non-parametric test should be applied. I have a concern about such practice. Let’s say the ...
168 views

### Why according to distribution graph it's normally distributed, but Jarque-Bera test shows non-normally distributed? [duplicate]

I am working on Kaggle's house pricing exercise and I cannot understand something. I watch and read articles on normality tests, and more specifically JB test, but I cannot understand why according to ...
158 views

### Is it possible to test for a Gaussian distribution? [duplicate]

Suppose that I have $n$ independent samples from a probability distribution. I believe that the distribution is Gaussian ($G$) but I don't know; then my question is: does there exist a test such that ...
70 views

### Normality test with p-value equal to zero [duplicate]

I have an array dataset of about 650.000 points. I want to test if the dataset follow a normal distribution or any other distribution. The first thing I did was to split the data in groups, find the ...
30 views

### What is exactly the non-normality requisite for nonparametric tests? [duplicate]

As the title says, what is exactly what is being tested before deciding to use a non-parametric alternative test (as Kruskal-Wallis for ANOVA, or Mann-Whitney's U for student's t)? Most sources are ...
41 views

### How to verify assumptions of a normal distribution? [duplicate]

I'm working with the iris data.I made a density plot And a qq plot For sepal Length.It looks Approximately normal With the left skew And a flat peak The points In the qq Plot Stay within The ...
36 views

### If the data is not normally distributed and the skewness is = 0.208 SE of skewness is 0.144 , is it acceptable to use t-test? [duplicate]

The sample size is 288 and by Shapiro- Wilk test the data is not normally distributed.
19 views

### Usefulness of rejecting null in normality test [duplicate]

In this Stackoverflow answer Ian Fellows said, Normality tests don't do what most think they do. Shapiro's test, Anderson Darling, and others are null hypothesis tests AGAINST the the ...
15 views

### testing normality for a two way anova, residuals as well as each sample? [duplicate]

to test a two way ANOVA do you have to test each sample for normality as well as normality for the residuals?
23k views

### What are common statistical sins?

I'm a grad student in psychology, and as I pursue more and more independent studies in statistics, I am increasingly amazed by the inadequacy of my formal training. Both personal and second hand ...
34k views

### Are large data sets inappropriate for hypothesis testing?

In a recent article of Amstat News, the authors (Mark van der Laan and Sherri Rose) stated that "We know that for large enough sample sizes, every study—including ones in which the null hypothesis of ...
101k views

### T-test for non normal when N>50?

Long ago I learnt that normal distribution was necessary to use a two sample T-test. Today a colleague told me that she learnt that for N>50 normal distribution was not necessary. Is that true? If ...
76k views

### How to choose between t-test or non-parametric test e.g. Wilcoxon in small samples

Certain hypotheses can be tested using Student's t-test (maybe using Welch's correction for unequal variances in the two-sample case), or by a non-parametric test like the Wilcoxon paired signed rank ...
3k views

### What are some examples of anachronistic practices in statistics?

I am referring to practices that still maintain their presence, even though the problems (usually computational) they were designed to cope with have been mostly solved. For example, Yates' ...
6k views

### When to use simulations?

So this is a very simple and stupid question. However, when I was in school, I paid very little attention to the whole concept of simulations in class and that's left me a little terrified of that ...
209k views

### How to perform a test using R to see if data follows normal distribution

I have a data set with following structure: a word | number of occurrence of a word in a document | a document id How can I perform a test for normal ...
5k views

### Is a distribution that is normal, but highly skewed, considered Gaussian?

I have this question: What do you think the distribution of time spent per day on YouTube looks like? My answer is that it is probably normally distributed and highly left skewed. I expect there is ...
70k views

### Regression when the OLS residuals are not normally distributed

There are several threads on this site discussing how to determine if the OLS residuals are asymptotically normally distributed. Another way to evaluate the normality of the residuals with R code is ...
2k views

### Distribution hypothesis testing - what is the point of doing it if you can't “accept” your null hypothesis?

Various hypothesis tests, such as the $\chi^{2}$ GOF test, Kolmogorov-Smirnov, Anderson-Darling, etc., follow this basic format: $H_0$: The data follow the given distribution. $H_1$: The data do not ...
2k views

### Test for finite variance?

Is it possible to test for finiteness (or existence) of the variance of a random variable given a sample? As a null, either {the variance exists and is finite} or {the variance does not exist/is ...
36k views

### Is it meaningful to test for normality with a very small sample size (e.g., n = 6)?

I have a sample size of 6. In such a case, does it make sense to test for normality using the Kolmogorov-Smirnov test? I used SPSS. I have a very small sample size because it takes time to get each. ...
5k views

### When does Fisher's “go get more data” approach make sense?

Quoting gung's great answer Allegedly, a researcher once approached Fisher with 'non-significant' results, asking him what he should do, and Fisher said, 'go get more data'. From a Neyman-Pearson ...
15k views

### Appropriate normality tests for small samples

So far, I've been using the Shapiro-Wilk statistic in order to test normality assumptions in small samples. Could you please recommend another technique?
24k views

### My distribution is normal; Kolmogorov-Smirnov test doesn't agree

I have a problem with the normality of some data I have: I've done a Kolmogorov test which says it isn't normal with p=.0000, I don't understand: the skewness of my distribution =-.497, and the ...
98k views

### What is the difference between the Shapiro-Wilk test of normality and the Kolmogorov-Smirnov test of normality?

What is the difference between the Shapiro-Wilk test of normality and the Kolmogorov-Smirnov test of normality? When will results from these two methods differ?
48k views

### How is Poisson distribution different to normal distribution?

I have generated a vector which has a Poisson distribution, as follows: x = rpois(1000,10) If I make a histogram using hist(x)...
19k views

### Factor analysis of questionnaires composed of Likert items

I used to analyse items from a psychometric point of view. But now I am trying to analyse other types of questions on motivation and other topics. These questions are all on Likert scales. My initial ...
17k views

### What tests do I use to confirm that residuals are normally distributed?

I have some data which looks from plotting a graph of residuals vs time almost normal but I want to be sure. How can I test for normality of error residuals?
15k views

### If my histogram shows a bell-shaped curve, can I say my data is normally distributed?

I created a histogram for Respondent Age and managed to get a very nice bell-shaped curve, from which I concluded that the distribution is normal. Then I ran the normality test in SPSS, with n = 169. ...
232k views

### How to check for normal distribution using Excel for performing a t-test?

I want to know how to check a data set for normality in Excel, just to verify that the requirements for using a t-test are being met. For the right tail, is it appropriate to just calculate a mean ...
26k views

### Normality of dependent variable = normality of residuals?

This issue seems to rear its ugly head all the time, and I'm trying to decapitate it for my own understanding of statistics (and sanity!). The assumptions of general linear models (t-test, ANOVA, ...
15k views

### Choosing between $z$-test and $t$-test

Background: I'm giving a presentation to colleagues at work on hypothesis testing, and understand most of it fine but there's one aspect that I'm tying myself up in knots trying to understand as well ...
4k views

### Which to believe: Kolmogorov-Smirnov test or Q-Q plot?

I'm trying to determine if my dataset of continuous data follows a gamma distribution with parameters shape $=$ 1.7 and rate $=$ 0.000063. The problem is when I use R to create a Q-Q plot of my ...
42k views

### Why do I get this p-value doing the Jarque-Bera test in R?

Doing a Jarque Bera test in R I get this result: jarque.bera.test(rnorm(85)) data: rnorm(85) X-squared = 1.259, df = 2, p-value = 0.5329 Does it mean that the ...
5k views

### Hypothesis Testing with Big Data

How do you perform hypothesis tests with big data? I wrote the following MATLAB script to emphasize my confusion. All it does is generate two random series, and run a simple linear regression of one ...
7k views

### Robust t-test for mean

I am trying to test the null $E[X] = 0$, against the local alternative $E[X] > 0$, for a random variable $X$, subject to mild to medium skew and kurtosis of the random variable. Following ...
20k views

### Regression - How do I know if my residuals are normally distributed?

Performing a regression and need to find out if my residuals are normally distributed.
32k views

### How to run two-way ANOVA on data with neither normality nor equality of variance in R?

I am working on my master thesis at the moment and planned on running the statistics with SigmaPlot. However, after spending some time with my data I came to the conclusion that SigmaPlot might not be ...
16k views

### Comparing two cumulative density functions

I am looking for a method to use to test for equality of two cumulative density functions.
40k views

### sample size too large? [duplicate]

I always thought larger sample sizes were better. Then I read something somewhere about how when sample sizes are larger, it's easier to find significant p-values when they're not really there (i.e., ...
25k views

### Estimating the distribution from data

I have a sample of data generated in R by rnorm(50,0,1), so the data obviously takes on a normal distribution. However, ...
4k views

### Normal Distribution or not?

I'm a newbie here. My question is the following. Are the following set of values normally distributed? 26, 33, 65, 28, 34, 55, 25, 44, 50, 36, 26, 37, 43, 62, 35, 38, 45, 32, 28, 34 The above values ...
15k views

### Checking residuals for normality in generalised linear models

This paper uses generalised linear models (both binomial and negative binomial error distributions) to analyse data. But then in the statistical analysis section of the methods, there is this ...
1k views

### Non-parametric alternative to simple t-test

I have five numeric variables of two populations (each of them with 60 individuals) and for each of those five variables I want to know if there is difference in the means. I was trying to use a ...
10k views

### QQ plot looks normal but Shapiro-Wilk test says otherwise

In R, I have a sample of 348 measures, and want to know if I can assume it is normally distributed for future tests. Essentially following another Stack answer, I am looking at the density plot and ...
7k views

### Testing the normality assumption for repeated measures anova? (in R)

So assuming that there is a point in testing the normality assumption for anova (see 1 and 2) How can it be tested in R? I would expect to do something like: ...