Question
Asked 8th Jun, 2021

When to use non-parametric testing with 2X2 within ANOVA?

I am running a within 2X2 ANOVA on SPSS. I have tested for normality prior and realised some of my conditions within a variable aren’t normally distributed. My question is say 1/4 conditions isnt normally distributed will I do a non-parametric test or ANOVA, same goes with the other way around if 1/4 is normal and rest aren’t do I do ANOVA Or non-parametric test. Trying to find papers which back up the reason why I am doing each test and struggling just really need a clear answer. Is it a majority rule kind of thing or is there set rules like taking outliers out that if one is not normally distributed it over-rules the others and I run that certain test with the 4 conditions (2X2) as a non-parametric test.

All Answers (3)

8th Jun, 2021
Blaine Tomkins
College of Saint Benedict and Saint John's University
Jayne Conlon What is the sample size per cell? ANOVA is robust to violations of normality, particularly when sample size is large. Take a look at the residual plot. To what extent do residuals deviate from normal? Only mildly or extremely?
If you haven't yet conducted the ANOVA, can you collect data from a few more participants? This might fix the problem. I do not recommend removing outliers unless there is strong theoretical reason for doing so - or there was an obvious error for a particular observation.
8th Jun, 2021
Jayne Conlon
Queen's University Belfast
The same size is small my thesis superviser has advice to remove outliers and to do within subjects 2X2 anova, however may be need for non parametric tests (if not normally distributed). For an example I’m testing a 360 turn test pre and post lecture condition and dance condition and it has shown that 1 of the 4 conditions isn’t normally distributed so for that variable I.e 360 turn test do I do the ANOVA or the non-parametric test. Blaine Tomkins
8th Jun, 2021
Blaine Tomkins
College of Saint Benedict and Saint John's University
Jayne Conlon I would probably use a nonlinear mixed effects model in this case. However, given that this is for a thesis an ANOVA will probably be fine. You could always do the ANOVA as planned, then do a nonparametric test with the data and see if the results of the two tests are consistent.

Similar questions and discussions

Recommendations

Article
Full-text available
Normal distribution is mostly used distribution in statistics, dating back to the Karl F. Gauss. It is used in many branches of statistics, however, testing for normality is not well understood. But which deviations from theoretical normality are still acceptable for a given statistical procedure? This contribution aims towards better understanding...
Preprint
Full-text available
Sample distributions provide clues about normality, which is a validity condition of t-and F-tests. Minor deviations from normality can have serious consequences for these tests whenever an additional validity condition (e.g., equal variances, equal sample sizes) does not hold. Additionally, a single outlier may badly distort the results of these t...
Article
Statistical models are often based on normal distributions and procedures for testing this distributional assumption are needed. Many goodness-of-fit tests suffer from the presence of outliers, in the sense that they may reject the null hypothesis even in the case of a single extreme observation. We show a possible extension of the Shapiro-Wilk tes...
The Impact of The Centre for Secure Information Technologies (CSIT)
Sponsored Content
The Centre for Secure Information Technologies (CSIT) is a national cybersecurity research institute based at Queen’s emphasising research excellence combined with a unique model for, and focus on, commercialisation and innovation.
CSIT plays a key role in Northern Ireland’s cybersecurity ecosystem through the development of incubator programmes, start-ups and attracting foreign direct investment which had led to the creation of approximately 1600 jobs in this sector.
CSIT's mission is to produce significant high-quality impactful research in four key research areas:
- Secure connected services
- Networked security systems
- Industrial control systems
- Security intelligence
CSIT couples major research breakthroughs in the field of secure information technologies with a unique model of innovation and commercialisation to drive economic and societal impact. Cyber security challenges have grown exponentially in the last decade. A safe and secure cyberspace is fundamental to making the UK the safest place in the world to live and work online.
Industry engagement is at the heart of CSIT. Its unique membership model has seen the development of longstanding advisory and industrial collaborations with global partners including Altera, Allstate, BAE Systems, Cisco, Citi, Direct Line Group, First Derivatives, IBM, Infosys, Intel, McAfee, Roke, Seagate and Thales. This unique Open Innovation model allows research to translate to industry in an agile way, ensuring demonstrable technology is in the hands of end users quickly.
Transforming the Lives of People with Cystic Fibrosis
Sponsored Content
Researchers from Queen’s have transformed the lives of people with Cystic Fibrosis by leading on the clinical development of treatments that address the underlying genetic disorder.
Cystic Fibrosis is a progressive, life-limiting genetic disease that causes severe respiratory and digestive problems as well as other complications such as infections and diabetes.
There are over 80,000 people living with Cystic Fibrosis globally, including 10,500 in the UK accounting for 9,500 hospital admissions and over 100,000 bed days per year.
The condition is caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene which is responsible for the regulation of salt and water levels in the body. The mutations can lead to the build-up of thick mucus in the lungs, digestive tract and other parts of the body causing persistent chest infections, resulting in lung damage and an early death.
Queen’s University’s Cystic Fibrosis research team is recognised as world leading, having worked for over 12 years supporting the development of drugs that improve the function of CTFR. during the last decade, Queen’s University Belfast has been at the forefront of major advancements in drugs targeting the underlying genetic deficit.
This work included the development of clinical trial protocols, and inclusion of key outcome measures such as; lung function (FEV1), pulmonary exacerbation rate, and Quality of Life (QoL) tools for use in clinical trials of new therapeutics.
Extensive clinical trial experience coupled with a Clinical Trial Network infrastructure established by Queen’s and the Belfast Health and Social Care Trust, resulted in Queen’s playing a pivotal role in a drug development programme working alongside Vertex Pharmaceuticals to deliver trials for single, double and triple therapies in Cystic Fibrosis.
1. There are over 80,000 people living with Cystic Fibrosis globally, including 10,500 in the UK - accounting for 9,500 hospital admissions and over 100,000 bed days per year.
2 The most recent trials successfully demonstrated that a combination of drugs can treat up to 90% of people with Cystic Fibrosis by addressing the underlying cause of their disease.
Got a technical question?
Get high-quality answers from experts.