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
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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
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0
answers
44
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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1
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81
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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
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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
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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
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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
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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 ...
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