Should we always choose a nonparametric test when comparing two apparently nonnormal distributions?

Journal of Clinical Epidemiology
Eva Skovlund, G U Fenstad

Abstract

When clinical data are subjected to statistical analysis, a common question is how to choose an appropriate significance test. Comparing two independent groups with observations measured on a continuous scale, the question is typically whether to choose the two-sample-t test or the Wilcoxon-Mann-Whitney test (WMW test). Similar results are often obtained, but which conclusion can be drawn if significance tests give highly different P-values? The t test is optimal for normally distributed observations with common variance and robust to deviations from normality if sample sizes are not very small. The WMW test makes no distributional assumptions, but depends heavily on equal shape and variance of the two distributions (homoscedasticity). We have compared the properties of the traditional two-sample t test, a modified t test allowing unequal variance, and the WMW test by stochastic simulation. All show acceptable behaviour when the two distributions have similar variance. When variances differ, the modified t test is superior to the other two.

Citations

Jun 28, 2011·Applied and Environmental Microbiology·Robert J AtterburyR Elizabeth Sockett
Apr 15, 2011·BMC Medical Research Methodology·Morten W FagerlandPetter Mowinckel
Jun 16, 2012·BMC Medical Research Methodology·Morten W Fagerland
Jan 10, 2012·Chemico-biological Interactions·Paul R SheppardMark L Witten
Dec 15, 2015·Journal of Molecular Graphics & Modelling·Rico Beier, Dirk Labudde
Mar 30, 2007·NeuroImage·Chris RordenThomas E Nichols
Sep 1, 2015·Toxicology in Vitro : an International Journal Published in Association with BIBRA·Nele Van den EedeTamara Vanhaecke
Jan 5, 2006·Journal of Clinical Nursing·Ragnhild Hellesø
May 8, 2013·The British Journal of Mathematical and Statistical Psychology·Isabel Parra-Frutos
Aug 19, 2014·American Journal of Obstetrics and Gynecology·Ometeotl AcostaThomas Jansson
Feb 28, 2009·Statistics in Medicine·Morten W Fagerland, Leiv Sandvik
Jun 14, 2015·Nephrology, Dialysis, Transplantation : Official Publication of the European Dialysis and Transplant Association - European Renal Association·Bernadette LiRommel Ravanan
Jun 7, 2014·Autism Research : Official Journal of the International Society for Autism Research·C Ellie WilsonDeclan G M Murphy
Sep 28, 2014·Annals of the Rheumatic Diseases·Stian Lydersen
Apr 22, 2016·Applied Neuropsychology. Adult·Heshmatollah GhawamiVafa Rahimi-Movaghar
Mar 23, 2002·Annual Review of Public Health·Thomas LumleyLu Chen
Jul 4, 2012·Lancet·Joshua Fogel, Vladimir Znamensky
Jan 9, 2010·Journal of Clinical Epidemiology·Markus Neuhäuser
Apr 6, 2017·Journal of Pediatric Orthopedics. Part B·Blazej PruszczynskiFreeman Miller
Mar 5, 2018·The Journal of Physiology·S Shekar DukkipatiSherif M Elbasiouny
Aug 30, 2017·Scandinavian Journal of Pain·Eva Skovlund, Harald Breivik
Jul 12, 2018·Journal of Interpersonal Violence·Gabriela López, Elizabeth A Yeater
Feb 6, 2016·Circulation Research·Lem Moyé
Mar 6, 2019·Journal of Clinical and Experimental Neuropsychology·Silke M MuellerElisa Wegmann
Jan 19, 2019·Archives of Gynecology and Obstetrics·Jiachen TangYu Chen
Apr 16, 2020·Journal of Neuroendocrinology·Marie-Luise BrandiLeonhard Schilbach
May 26, 2020·British Journal of Psychology·Xue Lei, David Perrett
Dec 9, 2016·Clinical Chemistry and Laboratory Medicine : CCLM·Marios A DiamantopoulosAndreas Scorilas
Oct 23, 2015·Journal of Pediatric Orthopedics·Mehmet S ErFreeman Miller
Aug 5, 2016·The International Journal of Pharmacy Practice·Angela MacAdamSian Williams
Dec 26, 2016·European Journal of Public Health·Gerlinde GrasserWillibald J Stronegger
Aug 2, 2020·The Canadian Journal of Cardiology·Dat T TranRobert Welsh
Mar 2, 2021·American Journal of Orthodontics and Dentofacial Orthopedics : Official Publication of the American Association of Orthodontists, Its Constituent Societies, and the American Board of Orthodontics·Burçin AkanRana Kızıltekin
May 14, 2021·Frontiers in Medicine·René LópezSuraj Samtani
Jun 3, 2021·International Journal of Environmental Research and Public Health·Ana Belén Barragán MartínJosé Jesús Gázquez Linares

Related Concepts

Related Feeds

Blood And Marrow Transplantation

The use of hematopoietic stem cell transplantation or blood and marrow transplantation (bmt) is on the increase worldwide. BMT is used to replace damaged or destroyed bone marrow with healthy bone marrow stem cells. Here is the latest research on bone and marrow transplantation.

Allogenic & Autologous Therapies

Allogenic therapies are generated in large batches from unrelated donor tissues such as bone marrow. In contrast, autologous therapies are manufactures as a single lot from the patient being treated. Here is the latest research on allogenic and autologous therapies.