All Questions
Tagged with nonparametric t-test
96
questions
1
vote
1
answer
57
views
Very small degrees of freedom when using yuen function in WRS2 package of R
I'm trying to run a number of independent samples t-tests. I'm using the yuen function in the WRS2 package because my data are non-normal and ordinal. My sample ...
- 13
3
votes
1
answer
695
views
I have applied many statistical tests to my data, but still cannot determine normality
I have run multiple tests to determine normality on my dataset, but I am unsure which one to adhere to, especially since my histograms, density plots, and QQ plots leave much to be desired in terms of ...
- 53
3
votes
1
answer
131
views
If I have a very small n for one group and a very large number of features, should I choose a parametric or a non-parametric test?
I have a dataset that contains human metabolite concetration in a fluid. One group has about 12 samples, while another only has 5. My question is if I can assume normality for this data and do ANOVA/t-...
1
vote
0
answers
44
views
Which Non-Parametric Test should I use?
I want to make sure I am choosing the right statistical test.
I am working with 7 semesters of exams scores for a particular course.
Each semester the course ran with many sections. However, the ...
- 11
2
votes
1
answer
513
views
Wilcoxon signed-rank test with an additional covariate
Problem formulation
I have 5 strains on which I administered treatment and repeated the experiment two times independently. So my data looks something like this:
...
- 165
0
votes
0
answers
87
views
Which statistical Test should I use/ Comparing 2 groups
I am new to statistics, can someone guide me regarding the test I should use to compare the foot dimensions of 9 subjects to footwear dimensions (we have 2 footwear brands).
So, to simplify, I have ...
1
vote
2
answers
82
views
Are t-tests good choices here?
I would like to test if two groups of participants (dark-eyed and light-eyed individuals) respond to a drug differently over time. The hypothesis is that the drug reaches its peak effects sooner but ...
- 13
2
votes
2
answers
296
views
Justification for conducting independent samples t test on non normal data
I've conducted a study comparing two different teaching strategies in two different sections of the same class; I gave participants in both classes the same 5 tests and wanted to see if test grades in ...
- 21
1
vote
1
answer
582
views
Welch's t test vs Mann-Whitney for very unequal groups
I have two vastly unequal groups (n1=18 and n2=400), and want to test mean differences between the groups for some 700 parameters (more specifically, RNA expression levels for 700 genes).
While I ...
- 33
0
votes
0
answers
82
views
Self-contradictory asumption of normality? Nonparametric point-biseral correltion coeffiicent? t-test or Mann-Whitney U?
A. I know from the net that for a design with one binary variable and a second variable that is continuous but is NOT normally distributed, I can use BOTH the point-biserial correlation (which is ...
- 1,363
2
votes
1
answer
138
views
How does violation of normality conditions affect p-values (relative to permutation tests)
I am running some t-tests using data from small samples (n=25) whose distributions do not appear to be normally distributed (they are not extremely skewed, but the skew is apparent in the plots and ...
0
votes
0
answers
39
views
Appropriate test for two not-normally-distributed data samples
I have some data comparing training participants who experienced the same training course either face-to-face or virtually (via Zoom). I have two survey items I am comparing. Sample A is for virtual ...
0
votes
1
answer
1k
views
Effect size for Welch's t-test
I ran an independent sample t-test to compare two groups, student sample and Mturk respondents. The homogeniety of variance was not met (variances are not equal and sample sizes of the two groups are ...
- 1
2
votes
2
answers
337
views
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 ...
- 361
0
votes
0
answers
64
views
Wilcoxon or T-test, paired, or unpaired? large data set, almost 1/2 are zeroes for habitat suitability values
Background I am just learning how to work with Spatial Distribution Models, these are basically regressions on environmental values and occurrence coordinates for a species. The result is a grid map ...
- 1
6
votes
3
answers
351
views
T-tests provide info about the margin of mean difference?
I have 2 unpaired datasets where the difference of the sample means is quite substantial (with the naked eye). The t-test shows that the difference is significant (p-value=0.007) and I would like to ...
- 63
0
votes
1
answer
345
views
Interpret Mann–Whitney U Test with highly skewed data
I have data for ~102,000 hands of bananas. The dataset has four data points:
Spiders present (True/False)
Count of rotten bananas in hand
Count of total bananas in hand
Percent of bananas that are ...
- 245
1
vote
0
answers
134
views
Tests for positively skewed data with large enough samples?
I'm new to statistic tests so I need a little bit of help with them. Most of my data has distribution similar to the histogram below.
As it can be seen from the histogram, the data is positively ...
2
votes
2
answers
43
views
Is there a way to quantify how appropriate a t-test is for given data?
I'm doing some programming and analysis for a post-doc who used to do this workflow using Excel and StatPlus. Apparently StatPlus has some feature where you tell it to compare two samples, and it will ...
- 241
4
votes
1
answer
164
views
T-Test or U-Test
I have a number of items that are based on a Likert scale, with values ranging from 1 = not at all to 5 = very much so. I would like to compare answers to these questions between two groups. I would ...
- 125
0
votes
0
answers
311
views
Wilcoxon signed rank test or t-test if data is highly skewed?
I have an variable that is highly skewed and I want to test whether my mean is equal to some fix value in another population. I only have the arithmetic mean of the other population. Because I prefer ...
- 227
1
vote
0
answers
670
views
Mann-Whitney U Test and Independent t-test give different results, which to use?
I have two population and I want to know if the means of the two populations are different. To the best of my knowledge, I should try an Independent t-test if the data is normality distributed and ...
- 65
3
votes
1
answer
74
views
Best tests for significance of relative risk
Currently I have insurance claim loss data (say roughly N=10,000), with independent variables state (California, Washington, etc.), policy number (uniquely identifies a policyholder), type of car (...
- 237
1
vote
1
answer
81
views
Is there any possible statistical test for this data?
I have a data set of the daily dosage of a drug that participants take against some signs and symptoms. The data are highly skewed to the left because there are a lot of patients with 0mg per day of ...
- 29
1
vote
0
answers
287
views
Testing for normality with small sample sizes in order to use t-test [duplicate]
I run into a conundrum when determining whether a small sample is appropriate for a t-test. I know that if I meet the assumptions, a t-test produces approximately correct inference with any sample ...
- 497
2
votes
2
answers
134
views
Which version of the t-test (or other) should I use?
UPDATE: I added histrograms and qqplots at the bottom.
A dataset of 1500 scores is close to being normally distributed, but is somewhat pointy, and is right-skewed. It has a mean of 500, and a ...
user179810
5
votes
2
answers
178
views
Wilcoxon (WMWU) test sensitivity
Statistics courses often give the Wilcoxon-Mann-Whitney U test ("Wilcoxon" from now on) as an alternative to the two-sample t-test.
However, the test is not quite the test of medians that would be so ...
- 65k
2
votes
1
answer
2k
views
Which statistical analysis should I perform if the data sets are not normally distributed?
I am doing an experiment where there are two independent groups; one is the group of "infected" patients another is the group of "sepsis" patients. I am comparing "platelet monocyte aggregates(PMA)" ...
1
vote
0
answers
46
views
Paired t-test on large sample that *should* be normal, but isn't (or Wilcoxon Signed Rank Test)?
A dataset contains the number of fast food restaurants per thousand people for each county in the USA, for two different years (five years apart). 3,143 rows.
None of the following are normally ...
user252085
1
vote
1
answer
722
views
How to find the difference between two set of scores of a single participant?
What I am trying to do?
I have a data set which consists of only one undergraduate student's all courses scores. Let's assume, he has completed about 70 courses where 40 courses are related to ...
- 294
0
votes
1
answer
34
views
Using paired t-test or Sign test to compare two groups of correlated measures on the same subject?
I have conducted a survey where participants are shown 8 different advertisements: 4 of the ads attempt to evoke the feeling of guilt, 4 others attempt to evoke the feeling of shame. After seeing each ...
0
votes
0
answers
1k
views
What statistical test is good for two groups of yes/no data set?
I have to detect certain bacteria and used two methods for same 200 samples. I have tabulated two methods as below:
...
- 101
1
vote
0
answers
132
views
What test to use when the dependent variable is an integer but independent variable is categorical? (Data non-normal, unequal variances)
My independent variable is species (categorical).
My dependent variable is the total mass of what each species ate (in grams, numerical).
I want to test the difference in mass values between ...
- 145
1
vote
1
answer
54
views
SPSS Chi square of one sample test
I am trying to analyze the following data: participants chose over 18 trials whether they would like option 1 or option 2. Option 1 is recoded as 0, option 2 is recoded as 1. Now if I count all ...
- 11
1
vote
1
answer
216
views
Variance in a T-test using means/medians
I have turning data for animals in different conditions with comparisons of before and after these conditions, we'll say condA condB.
Each animal has 3 repeats on both conditions, where before a ...
- 127
1
vote
1
answer
371
views
Interpreting a significant correlation in a small sample
I found a correlation between two variables:
Variable A is dichotomous, with values 1 and 2 (for yes/no)
Variable B is continous (score, 0 - 50)
They correlated with each other. However, my sample ...
- 113
0
votes
1
answer
71
views
How to calculate a 𝑝-value for the difference between two non normal distributions of counts?
I have two NON normal distributions (a and b), they are also different lengths
...
- 101
0
votes
0
answers
57
views
Do we need parametric tests? [duplicate]
First of all, sorry for catchy title, my question is not that broad as it suggests.
I just came to conclusion that I don't need parametric tests. Instead, I need some feedback if my reasoning makes ...
- 4,091
1
vote
0
answers
36
views
2 sample t test
I was thinking that a simple 2 sample t test is not that simple when dealing with skewed data.
Considere 2 samples, each one with diferent skewness and kurtosis, both with a big sample sizes (say n > ...
- 561
1
vote
2
answers
696
views
Under what circumstances does Mann-Whitney and Wilcoxon signed-rank test fail?
I read from here that
The advice must be modified somewhat when the distributions are both strongly skewed and very discrete, such as Likert scale items where most of the observations are in one of ...
- 1,041
0
votes
1
answer
553
views
Significance test with non-normal, bounded data?
I am attempting to do a one-sample significance test to determine whether a set of data differs from a given value (0 in this case). The issues I have with these data:
Non-normally distributed data, ...
- 3
3
votes
3
answers
1k
views
Papers About Permutation Version of Welch's t-test
Permutation tests seem to provide a promising alternative for the unpaired t-test, requiring fewer assumptions. However, the core assumption of the permutation test, exchangeability, implies ...
1
vote
2
answers
404
views
Appropriate statistical test for data which do not have normally distribution and do not have equal variance
My data has 150 samples and is not normally distributed, and it does not have equal variances either. I know t-test (e.g. this python method) can be used when data is normally distributed and it can ...
- 271
1
vote
0
answers
28
views
Alternative test to paired t-test? [duplicate]
I need to compare data from paired groups, but my distributions are non-normal, and my sample size is small. Are there any tests I could apply?
I've been looking into non-parametric alternatives like ...
- 11
1
vote
2
answers
122
views
Which statistic test should I use in this situation?
There are 10 questions in which we are comparing peoples' opinion about two conditions, "X"and "Y". Every question was answered by about 90 people who were different than other questions' respondents. ...
- 145
2
votes
1
answer
5k
views
Paired t-test of a non-normal data with sample size 66
I have a paired data with n=66. I understand that normality condition of differences data should be met to conduct a paired t-test. However, from the histogram, it doesn't appear so normal. The p-...
- 135
7
votes
3
answers
9k
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 ...
1
vote
0
answers
45
views
Non parametric tests for relation/association between variable
What could be an appropriate test for checking whether there exist any relationship between Net Promoter Score ( Categorical in nature with 0 meaning detractor, 1 meaning Neutral, 2 meaning Promter ) ...
- 111
3
votes
1
answer
288
views
Is the $t$-test asymptotically nonparametric?
Wikpedia defines "parametric statistics" as:
...a branch of statistics which assumes that sample data comes from a
population that follows a probability distribution based on a fixed
set of ...
- 3,750
1
vote
1
answer
226
views
Should I use non-parametric tests?
I am a teacher working on a simple research with the aim of studying whether the set of lesson designs I created can improve student performance. I have two groups with 15 students each. I divided ...
