Tagged Questions

1
vote
1answer
87 views

All my observations are identical. Use a non-parametric test?

I was doing test for normality on variables and came across one that had identical values for each observation. I can't do a normality test. I plotted the kernel density and it looks normal, however ...
2
votes
2answers
211 views

Mann-Whitney for non-normal distributions with n>20?

I have 12 groups of datasets (mostly non-Normal, quite right-skewed), and I would like to see if there is a significant difference within each pair. (But the data itself is not a paired dataset, as in ...
0
votes
0answers
65 views

Test for significance for multiple non-normally distributed samples

I was wondering if anyone could point me in the right direction for what exactly I'm looking for. I have binned multiple Boolean observations (1 or 0). The reason I made them Boolean is because it's ...
1
vote
1answer
261 views

Comparing P value from t test vs. Mann-Whitney test

If you analyze the same data with a t test and the nonparametric Mann-Whitney test, which do you expect to have the lower P value?
2
votes
4answers
1k views

Which test to choose when the results from t-test and Wilcoxon test are different?

I have a sample of 48. According to the central limit theorem, I may consider means of every continuous variable in my sample to have a normal distribution. However, one variable has a mean of 14 +/- ...
0
votes
1answer
264 views

Whether to use nonparametric tests to compare two groups when sample size is large but assumptions are violated

I have a data set that has 600 observations divided in two groups. I am going to compare the central tendencies (e.g., the means) of these two groups. However, there are violations of classical ...
1
vote
2answers
419 views

Why would I use ANOVA instead of a Rank-Sum test?

A colleague of mine with little statistics experience is trying to perform an experimental evaluation of a computer program. He created a between subjects design and solicited test subjects. 11 ...
5
votes
3answers
5k views

What is a minimum sample size for a paired t-test and what is a non-parametric equivalent if data is non-normal?

I have 4 sample pairs, let's say (x1, y1),...,(x4, y4). What is the minimum sample size for a paired t-test? Which assumption should I check for paired t-test? If my data is non-normal, what is an ...
19
votes
5answers
6k views

Which permutation test implementation in R to use instead of t-tests (paired and non-paired)?

I have data from an experiment that I analyzed using t-tests. The dependent variable is interval scaled and the data are either unpaired (i.e., 2 groups) or paired (i.e., within-subjects). E.g. ...