All Questions
Tagged with nonparametric normality-assumption
52
questions
2
votes
2
answers
370
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How could Lilliefors use Monte Carlo if the estimand is not distribution-free?
Lilliefors test is a well-known statistical test for normality. Its idea is based on the Kolmogorov-Smirnov test, except the CDF is replaced by the CDF of the normal distribution with $\mu, \sigma^2$ ...
- 235
3
votes
1
answer
695
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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
0
votes
0
answers
31
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Anova violates normality assumption for error data
I have a 2 x 2 repeated measures ANOVA (N = 51) with Error Rate data as the dependent measure. The error data violates the normality assumption, even when outliers are removed. I have looked at the ...
- 113
0
votes
0
answers
67
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Comparing non-normal data between three groups
I am analyzing a dataset, where I have 3 categories (independent variable), and one continuous value (dependent variable). I am studying if the continuous value is significantly different between the ...
- 21
2
votes
2
answers
115
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Distribution and variable analysis
I am doing a statistical test (program used is SPSS). On the basis of distribution and sample size, I have to chose the correct variable analysis. I also have to justify every decision. I have two ...
- 21
0
votes
1
answer
57
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Importance of normality testing in clinical trials / AB tests
I’m curious to read about the importance of normality testing in AB tests and clinical trials.
It seems that there is a lot of mixed (and strong) opinions about the necessity for normality testing, ...
- 67
0
votes
1
answer
429
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Testing for normality of difference between pre-post scores
I'm currently trying to decide what test to run on SPSS for my data. I am comparing the effects of 3 different interventions on trauma scores. I have both pre and post-scores.I have created a ...
- 1
2
votes
1
answer
70
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Alternatives to ANOVA to find differences between three groups?
So my data is looking at the incidence of emotions within therapy sessions. I am looking at three groups that I suspect have different pattern across several emotions
Group 1 n=36
Group 2 n=12
Group 3 ...
- 21
1
vote
0
answers
15
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Looking for associations between nominal and non-parametric continuous data
I'm a first-year BSc Biology student working on my end-of-module stats project, so that's the expected level of my work.
I need to find associations between hindlimb length and frog locomotor modes (e....
- 11
1
vote
1
answer
241
views
Which statistical test should I use if the assumptions of a 2-way ANOVA are not met?
My study design consists of two factors (one with 2 levels, the other with 6) and a continuous response variable. In order to analyze the influence of both factors on the explanatory variable I built ...
- 441
3
votes
3
answers
149
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Problem with a single outlier, non-normal data, and unequal sample distributions
I am wanting to compare two independent groups on a likert-like item. To explain, the dependent variable is structured so that a 1 = <1 units, 2 = 1-<2, 3 = 2-<3, all the way up to option 7 = ...
- 31
0
votes
0
answers
275
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How can I perform a Tetrachoric and Polychoric Correlation on variables that aren't normally distributed?
From everything I have read, both tetrachoric and polychoric correlations assume normal distributions. However, the data I want to conduct these correlations with is not normally distributed. Does ...
- 101
3
votes
2
answers
975
views
Does aligned rank transform ANOVA require normally distributed data?
Initially, I wanted to do a two-factorial (4x3) repeated measures ANOVA in order to analyse my data.
To be more precise, I do have two factors with factor1 having 4 levels (A, B, C, D), factor2 having ...
- 31
0
votes
0
answers
175
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Is there a non-parametric test to replace repeated-measures ANOVA in R?
I have a data set with 41 individuals, male and female, and 3 different measurements of a variable for each individual. The data is not normally distributed, nor does it have equal variances between ...
6
votes
2
answers
8k
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Can we ALWAYS assume normal distribution if n >30?
I'm in a debate with a coworker and I'm starting to wonder if I'm wrong but the internet is confusing me more.
We have continuous data $[0, \infty)$ that is retrospectively selected on individuals. ...
- 185
1
vote
0
answers
106
views
Bounds for hypothesis testing with non-normal distributions
After doing randomized experiment with two variants (AB tests), I want to do hypothesis testing without the normal distribution assumption to compare their means. Since the samples sizes are different,...
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
1
vote
2
answers
3k
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Multiple comparisons for not normal and heterogeneous data
I have a data set that has 3 groups and a single variable. Under normal circumstances, a one-way ANOVA would be used for comparisons between my three groups. HOWEVER I ran a Shapiro-Wilk test for ...
0
votes
0
answers
50
views
Parametric v Non-Parametric?
I've recently began doing some data analysis for a sample of around 5800 respondents who are categorised into four different groups in relation to different levels of psychological connection in a ...
- 1
1
vote
0
answers
144
views
Coverage of confidence interval of non-normal distribution
I know that when a sample is non-normally distributed, I need to use non-parametric alternatives, as when the assumptions of parametric methods are violated, its coverage will decrease.
Let's say ...
- 1,041
0
votes
1
answer
584
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What is exactly the non-normality requisite for nonparametric tests? [duplicate]
As the title says, what is exactly what is being tested before deciding to use a non-parametric alternative test (as Kruskal-Wallis for ANOVA, or Mann-Whitney's U for student's t)?
Most sources are ...
- 1,472
0
votes
1
answer
213
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Normality Tests in samples with outliers
I'm making a code in R that contains some parametric and non-parametric tests, like ANOVA and Kruskal-Wallis.
To know if I should use one or another I check the "normality" of the test sample. My ...
3
votes
3
answers
2k
views
Tests of normality - qq and Shapiro-Wilk
I am new to the world of stats ...
My data had a log normal distribution, so transformed by log to get it nearer normal distribution. This is real-world data.
From here I want to establish if my data ...
6
votes
2
answers
3k
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Wilcoxon Test - non normality, non equal variances, sample size not the same
I know there are already a lot of posts out there, but I couldn't find this exact combination in any of them.
Comparing two samples (Prices associated with men and with women), but I have neither the ...
- 71
2
votes
1
answer
382
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Meta analysis Cliff's delta
Cliff's delta is an effect size typically recommended whenever the normality and homogeneity assumption do not hold---and thus, Cohen's d cannot be used.
However, I cannot see any reference ...
- 157
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
3
votes
1
answer
5k
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Two-Way Non-Parametric Test for Non-normal Data?
I have an unbalanced design with two factors, gender and site. I'm trying to test for differences in a size variable. Levene's test reveals that the data has equal variances. However, log transformed ...
- 45
3
votes
2
answers
2k
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Theil-Sen estimator assumptions
I found by accident the nonparametric Theil-Sen Estimator as a replacement for standard OLS linear Regression. How well does it perform with autocorrelated data, non-normal residuals and ...
- 69
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 ...
0
votes
1
answer
359
views
Do I need to check for normality in a one-way test (in R)?
http://www.sthda.com/english/wiki/one-way-anova-test-in-r
Here it says when the LeveneTest has small p-value we can use the alternative one
...
J.Doe
0
votes
1
answer
35
views
From what size considering that the sample is large and allows to use the parametric tests
With a large sample size we can used a parametric test whithout testing a normality of distribution. from what size can we consider that the size of the sample is large?
- 171
0
votes
1
answer
3k
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Normality test for likert scale [duplicate]
I have a questionnaire data that consist of composite Likert scale and discrete Likert items.
Likert scales or variables are the sum of few Likert items while the one-item variables are represented ...
1
vote
1
answer
8k
views
Transforming positively skewed data with positive and negative values
My data (see image below) is positively skewed and contains both positive and negative values. I'd like to transform it to achieve normality so I can apply a repeated measures ANOVA, but can't find a ...
- 43
0
votes
0
answers
933
views
Normally distributed data but small sample size, use nonparametric test?
My data set is very small (n=16) which according to a Shapiro-wilk test is normally distributed (p=0.82), despite the histogram looking questionable. When I split the data into my two categories there ...
1
vote
1
answer
111
views
Normality in ANOVA
I have an independent variable with 4 levels. Lets say Group A, B, C and D.
When i see for the normality in my dependent variables, i can see, some dependent variables are normal in Group A, B and C ...
- 11
1
vote
2
answers
996
views
what is the meaning of 'normality' as a difference between parametric and nonparametric method? [duplicate]
I'm so confused of the definition of the terminology, "normality". I mean, normality of what?
According to central limit theorem, regardless of the distribution of population,the computed values of ...
- 449
7
votes
2
answers
1k
views
Is the inference from a parametric test valid when the population distribution is not normal?
This question arose from reading this post: T-test for non normal when N>50?
In the response to this post, the author outlines really well that the assumption of normality with regard to the t-...
- 71
7
votes
2
answers
12k
views
Non-Parametric altervative to one sample t-test
I have a the following hypothesis: $H_0: \mu=4$, $H_1: \mu\neq 4$, which I wanted to test using a one sample t-test.
However, my data is not normally distributed and a transformation was not found. ...
- 486
2
votes
0
answers
57
views
group comparisons - normality of the distribution
When comparing 3 different groups on a certain variable and one of the groups does not have a normal distribution (as verified by the Shapiro test) whilst the other to do, would you think it is best ...
- 305
2
votes
2
answers
196
views
Most appropriate analysis for non-normal, right-censored response variable?
I conducted an experiment with human subjects in which the independent variable has 3 treatment levels and the dependent variable is the duration of time that passes before the subject engages in a ...
- 480
1
vote
0
answers
143
views
Four standard deviation rules in relation to normality testing
Within our department we were given a set of guidelines for how we might decide whether to proceed with parametric or non-parametric testing (for continuous data). These were drawn up in consultation ...
- 11
6
votes
2
answers
370
views
What is an example of data where the permutation test succeeds but a normal t-test fails?
In literature, I normally see authors use a two sample permutation test on normal data to show that it works as well as the two sample t-test. However, the real power for permutation tests should be ...
- 2,107
1
vote
1
answer
9k
views
Using ANCOVA when the covariate is not normally distributed
I have conducted a repeated-measures ANOVA, but a reviewer suspects that the observed main effect of condition are due to a the difference between hit rates of two conditions (one of them is ...
- 11
1
vote
1
answer
138
views
Total scores are normally distributed, but subtest scores are not; what to do?
I have two sets of data for males and females: $n=33$. I'd like to compare test results for both groups. I want to do a $t$ test, and I know my data should be normally distributed if I want to use a ...
- 231
3
votes
0
answers
76
views
Comparison of cell counts with a right censoring
I have cell counts related to the action of different microorganisms and I want to compare their distribution. It's supposed they follow a normal distribution after a log transformation, but I can't ...
- 75
0
votes
2
answers
2k
views
Absolute values -- parametric or non-parametric test?
I am looking at the absolute difference in values between pairs of numbers. I am then comparing these absolute values between two groups (e.g. Males and Females). Since these are absolute values I ...
- 1
0
votes
1
answer
2k
views
What statistical test to use for my questionnaire
I have to do some statistical tests on a questionnaire and don't know which tests i need to do. The questionnaire have been marked as right or wrong and I have about 60 peoples results. The tests i ...
1
vote
1
answer
262
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 ...
- 157
4
votes
3
answers
13k
views
Normality assumption and sample size
I know this is a very debated topic, even on this site, but I still couldn't find an answer to my problem.
Recently I am working with large samples (300, 400 and more). For now, I am trying to use ...
- 115
2
votes
0
answers
123
views
Which statistical method of anlysis should I use?
I am conducting an experiment where I will measure the strength of a material used for roads. Ideally, I would like to use a large surface area to measure this but this takes too long and is really ...
- 1,135