Abstract
In randomized clinical trials of antiepileptic drugs (AEDs), the seizure frequency per x days during baseline and treatment phase periods are recorded to evaluate efficacy of a drug. The seizure frequency data are often nonnormal, and hence an appropriate mathematical transformation is necessary for a statistical analysis. The most commonly used transformations in AED development research are (a) log-transformation of the seizure frequency data, and (b) calculation of percentage change (PC) from baseline in seizure frequency. The log-transformed postbaseline seizure frequency data are analyzed using a parametric ANCOVA model including the log-transformed baseline data as a covariate and treatment group as a factor in the model. The PC data are analyzed using either a Wilcoxon rank-sum test on the PCs, or ANOVA/ANCOVA analysis on the ranks of PCs including treatment groups as a factor and any covariate of interest in the model. A limited number of research works is available in the literature regarding a choice of log-transformed or PC of seizure frequency data in the statistical analyses. In this research, an attempt is made to evaluate the impacts of choosing either of the two transformations on seizure frequency data of AED trials.
Similar content being viewed by others
References
European Agency for the Evaluation of Medicines. Note for guidance on clinical investigation of medicinal products in the treatment of epileptic disorders. 2000. CPMP/EWP/566/98.
Vickers AJ. The use of percentage change from baseline as an outcome in a controlled trial is statistically inefficient: a simulation study. BMC Med Res Methodol. 2001;1:6.
Berry DA. Statistical Methodology in the Pharmaceutical Sciences. New York: Marcel Dekker; 1989:37–39.
Koti KM. On a primary efficacy endpoint. Drug Inf J. 2001;35:157–162.
Berry DA, Ayers GA. Symmetrized percent change for treatment comparisons. Am Stat. 2006;60(1):27–31.
Berry DA. The consultant’s forum: logarithmic transformations in ANOVA. Biometrics. 1987;43:439–456.
Carroll RJ. A robust method for testing transformations to achieve normality. J R Stat Soc B. 1980;42:71–78.
Conover WJ, Iman RL. Analysis of covariance using the rank transformation. Biometrics. 1982:38:715–724.
Laird N. Further comparative analyses of pretest-posttest research designs. Am Stat. 1983;37:329–330.
Madsen L, Dalthorp D. Simulating correlated count data. Environ Ecol Stat. 2007;14:129–148.
Kaiser L. Adjusting for baseline: change or percentage change? Stat Med. 1989;8:1183–1190.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Siddiqui, O., Hershkowitz, N. Primary Efficacy Endpoint in Clinical Trials of Antiepileptic Drugs: Change or Percentage Change. Ther Innov Regul Sci 44, 343–350 (2010). https://doi.org/10.1177/009286151004400316
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1177/009286151004400316