Comparison of Paired T-Test and Wilcoxon Signed Rank Test for Various Change Measures in Pre-Post Designs: A Simulation Study

Ankarali, Handan; Yilmaz, �zge; Aydin, Duygu
September 2012
Turkiye Klinikleri Journal of Biostatistics;2012, Vol. 4 Issue 2, p55
Academic Journal
Objective: In a pre-post design, most commonly used change measure is simple difference (D), but percent change (PC) and symmetrized percent change (SPC) are not. We aimed to determine whether paired t-test and Wilcoxon signed rank test are suitable for PC and SPC according to type-I error and the power by a simulation. Material and Methods: Simulation study was performed by using normally distributed random numbers. Two samples which were called pre and post treatment measures with replacement were taken from a standard normal population which included 10,000 observations. Three different sample size, two different correlation degree, two different standard deviation and two different effect sizes were investigated for the purposes in simulation study. Results: The actual type- I error probabilities of paired t-test for PC were higher than nominal level except variances of pre and post measurements were near to homogenous. But they were observed significantly different from its nominal level in all test combinations for SPC. Actual type-I error of WSR for PC and SPC were found different from 5% when sample size is lower than 20. The powers of t-test and WSR test for PC and SPC were also low or mode rate level in the simulation conditions. Conclusion: PC and SPC measures should only be used for descriptive purposes until appropriate test will found.


Related Articles

  • A New Maximum Test via the Dependent Samples t-Test and the Wilcoxon Signed-Ranks Test. Maggio, Saverpierre; Sawilowsky, Shlomo S. // Applied Mathematics;Jan2014, Vol. 5 Issue 1, p110 

    A maximum test in lieu of forcing a choice between the two dependent samples t-test and Wilcoxon signed-ranks test is proposed. The maximum test, which requires a new table of critical values, maintains nominal α while guaranteeing the maximum power of the two constituent tests. Critical...

  • Correcting Two-Sample z and t Tests for Correlation: An Alternative to One-Sample Tests on Difference Scores. Zimmerman, Donald W. // Psicológica;2012, Vol. 33 Issue 2, p391 

    In order to circumvent the influence of correlation in paired-samples and repeated measures experimental designs, researchers typically perform a one-sample Student t test on difference scores. That procedure entails some loss of power, because it employs N - 1 degrees of freedom instead of the...

  • Randomized controlled trial on the effect of coaching in simulated laparoscopic training. Cole, Simon; Mackenzie, Hugh; Ha, Joon; Hanna, George; Miskovic, Danilo // Surgical Endoscopy;Mar2014, Vol. 28 Issue 3, p979 

    Background: The effect of coaching on surgical quality and understanding in simulated training remains unknown. The aim of this study was compare the effects of structured coaching and autodidactic training in simulated laparoscopic surgery. Methods: Seventeen surgically naive medical students...

  • New Procedure in Testing Differences between Two Groups. Ahad, Nor Aishah; Othman, Abdul Rahman; Soaad Syed Yahaya, Sharipah // Applied Mathematics & Information Sciences;Jun2013 Special Issue, Vol. 7, p397 

    Despite the theoretical correctness of the t-test in testing differences between two groups and the existence of the nonparametric backup, i.e. Mann-Whitney-Wilcoxon test, these test fail to simultaneously control Type I error and maintain adequate power under certain condition. This study...

  • Cycle Outcome for Women with Bilateral Endometriomas.  // Fertility Weekly;6/24/2013, p8 

    The article presents a study which examines the outcome of in vitro fertilization (IVF) in women with bilateral endometriomas. The study uses ultrasound, student t-test, and nonparametric Wilcoxon unpaired test to determine the effect of bilateral endometriomas in the quality of the oocytes and...

  • An evaluation of statistical methods for DNA methylation microarray data analysis. Dongmei Li; Zidian Xie; Le Pape, Marc; Dye, Timothy // BMC Bioinformatics;Jul2015, Vol. 16 Issue 1, p1 

    Background: DNA methylation offers an excellent example for elucidating how epigenetic information affects gene expression. β values and M values are commonly used to quantify DNA methylation. Statistical methods applicable to DNA methylation data analysis span a number of approaches such as...

  • Performance of the Modified Wilcoxon Signed Rank Test. Ahad, Nor Aishah; Syed Yahaya, Sharipah Soaad; MdYusof, Zahayu; Abdullah, Suhaida; Lim Yai Fung // AIP Conference Proceedings;2014, Vol. 1635, p690 

    Nonparametric methods require only few assumptions to be made about the format of the data, and they may therefore be preferable when the assumptions required for parametric methods are not valid. The Wilcoxon signed rank test applies to matched pairs studies. For two tail test, it tests the...

  • Efectos de la entrevista motivacional en el tratamiento de la diabetes mellitus tipo 2. García Flores, Raquel; Sánchez Sosa, Juan José // Revista Psicología y Salud;jul-dic2013, Vol. 23 Issue 2, p183 

    No abstract available.

  • Rehabilitation After Surgery Repair of Flexor Tendon Injuries of the Hand with Kleinert early Passive Mobilization Protocol. Hundozi, Hajrie; Murtezani, Ardiana; Hysenaj, Vale; Hysenaj, Vlore; Mustafa, Aziz // Medical Archives / Medicinski Arhiv;Apr2013, Vol. 67 Issue 2, p115 

    Introduction: Rehabilitation after surgery repair of flexor tendon injuries of the hand remains challenging and requires experienced professionals and interdisciplinary approaches. Aim: The aim of this study was to evaluate rehabilitation results after surgery repair of flexor tendon injuries in...


Read the Article


Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics