All Questions
Tagged with nonparametric normality-assumption
52
questions
2
votes
2
answers
370
views
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
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
0
votes
0
answers
31
views
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
views
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
views
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
views
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
views
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
views
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
views
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
views
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
views
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
views
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
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
1
vote
2
answers
3k
views
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
views
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
views
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
views
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
views
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
views
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
views
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