Linked Questions
77 questions linked to/from How to choose between t-test or non-parametric test e.g. Wilcoxon in small samples
2
votes
1
answer
10k
views
t-test using a sample less than 30 [duplicate]
When I do the two tailed t-test using a sample less than 30, can I use this result? This is because I do also still see the t-test table which has degrees of freedom far less than 30. How further ...
- 424
1
vote
0
answers
881
views
Unpaired t-test: large samples, unequal variances, unequal sample sizes [duplicate]
I a have two independent samples one with more than 700 observations and the second with more than 500 observations. I firstly use Cramér-von Mises test to test normality just to check how non-normal ...
- 41
1
vote
1
answer
677
views
Should I use the t-test or the Wilcoxon rank sum test given these qqplots and Shapiro-Wilk stats [duplicate]
I have 4 groups and I want to test if the pairwise difference in means are significantly different. There are 6 pairwise differences.
The QQnorm plots of the 4 groups look like this:
The Shapiro-...
- 163
2
votes
0
answers
435
views
Need and best way to determine normality of data [duplicate]
I believe there are many ways to determine if data is normal or not:
histogram shape
QQ plot
skewness
kurtosis
shapiro test.
Which of the above is the best way to determine if data is normal and ...
- 9,259
1
vote
1
answer
203
views
Is it valid to conduct t-tests with just 20 students? [duplicate]
By reading article I think I found a bug:
Seams to me that 20 is a very small number of samples in this article assuming 20 students are taken random and the order of students is not important. I ...
- 304
0
votes
0
answers
335
views
Test statistics in IR (t-test vs Wilcoxon vs signed test) [duplicate]
I have just read this paper about different test statistics one could use in Information Retrieval (IR), discussing whether Wilcoxon, Sign-test or Student t-test would be more reliable for comparing ...
- 205
3
votes
0
answers
131
views
T-test for a small sample with unknown distribution [duplicate]
Consider a simple hypothesis test concerning the mean of a single sample.
If the sample is normally distributed and the variance is known, the exact distribution of the sample mean is known ($N$~$(\...
- 1,736
367
votes
15
answers
136k
views
Is normality testing 'essentially useless'?
A former colleague once argued to me as follows:
We usually apply normality tests to the results of processes that,
under the null, generate random variables that are only
asymptotically or ...
- 14.1k
113
votes
7
answers
187k
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 ...
- 2,257
76
votes
15
answers
11k
views
Why would parametric statistics ever be preferred over nonparametric?
Can someone explain to me why would anyone choose a parametric over a nonparametric statistical method for hypothesis testing or regression analysis?
In my mind, it's like going for rafting and ...
- 927
57
votes
10
answers
4k
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' ...
53
votes
8
answers
36k
views
When conducting a t-test why would one prefer to assume (or test for) equal variances rather than always use a Welch approximation of the df?
It seems like when the assumption of homogeneity of variance is met that the results from a Welch adjusted t-test and a standard t-test are approximately the same. Why not simply always use the Welch ...
- 17.6k
99
votes
2
answers
14k
views
How much do we know about p-hacking "in the wild"?
The phrase p-hacking (also: "data dredging", "snooping" or "fishing") refers to various kinds of statistical malpractice in which results become artificially statistically significant. There are many ...
- 21.6k
27
votes
4
answers
17k
views
Practically speaking, how do people handle ANOVA when the data doesn't quite meet assumptions?
This isn't a strictly stats question--I can read all the textbooks about ANOVA assumptions--I'm trying to figure out how actual working analysts handle data that doesn't quite meet the assumptions. I'...
- 798
28
votes
5
answers
20k
views
How robust is the independent samples t-test when the distributions of the samples are non-normal?
I've read that the t-test is "reasonably robust" when the distributions of the samples depart from normality. Of course, it's the sampling distribution of the differences that are important. I have ...
- 585