Linked Questions

6
votes
3answers
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 ...
12
votes
2answers
11k 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 ...
11
votes
5answers
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: ...
10
votes
2answers
15k views

“Ties should not be present” in one-sample Kolmgorov-Smirnov test in R

I am going to use the Kolmogorov-Smirnov test to test normality of MYDATA in R. This is an example of what I do ks.test(MYDATA,"pnorm",mean(MYDATA),sd(MYDATA)) ...
11
votes
1answer
17k views

Testing large dataset for normality - how and is it reliable?

I'm examining a part of my dataset containing 46840 double values ranging from 1 to 1690 grouped in two groups. In order to analyze the differences between these groups I started by examining the ...
7
votes
5answers
12k views

How to determine whether data is slightly or extremely non-normally distributed?

I'm a PhD student and doing a research on regression analysis. My question is how to determine whether the data is slightly, moderately or extremely non-normally distributed? TQ to all responses of ...
23
votes
1answer
3k views

Is a priori power analysis essentially useless?

I attended a meeting of the Society for Personality and Social Psychology last week where I saw a talk by Uri Simonsohn with the premise that using an a priori power analysis to determine sample size ...
5
votes
2answers
6k views

Should the Shapiro-Wilk test and QQ-Plot always be combined?

I have read multiple places that Shapiro-Wilk test should always be added with a QQ-plot, but no one has given a reason, and I do not see the intuition behind this. Can anyone explain why one need to ...
0
votes
4answers
6k views

Mann-Whitney or t-test to compare age and expenditure after clustering

I have carried out cluster analysis and now want to compare means between variables in different clusters. The variables in question are age and expenditure in millions of dollars. The age variable ...
7
votes
4answers
4k views

What practical implications/interpretations are there of a kurtotic distribution?

I'm familiar with what the 2nd moment (variance) indicates as well as what the 3rd moment (skewness) indicates. I know that on a histogram the 4th moment (kurtosis) indicates the "peeked-ness" of the ...
11
votes
3answers
1k 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 ...
7
votes
2answers
9k views

Testing normality

I have a large dataset (500000 data, V1 column include all the data). x <- read.csv("mydata.csv", header=F) hist(x) Which gives: Looking at the data, I ...
3
votes
2answers
3k views

How far can be median, mode and mean be from each other and still be able to say that is a normal distribution?

I'm working on the Boston housing project of the udacity ML nano degree. A histogram of the data set looks like this: The mean, median and mode are: ...
8
votes
2answers
4k views

Non-normality in residuals

I refer to this post which seems to question the importance of the normal distribution of the residuals, arguing that this together with heteroskedasticity could potentially be avoided by using ...
4
votes
2answers
7k 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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