The Number of Centers in a Multicenter Clinical Study: Effects on Statistical Power
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Drug Information Journal, Vol. 34, pp. 379-386, ZOO0 Printed in the USA. All rights reserved.
Copyright 0 2000 h g Information Association Inc.
THE NUMBER OF CENTERS IN A MULTICENTER CLINICAL STUDY EFFECTS ON STATISTICAL POWER ZHENGNING LIN,PHD Senior Biostatistician, Medical Information Processing and Statistics, Novartis Pharmaceuticals Corporation, East Hanover, New Jersey
In the pharmaceutical industry it is often important to ensure fast patient enrollment. A common practice to speed up patient enrollment is to use more clinical centers. One of the concerns regarding this practice is that increasing the total number of centers to a certain degree may decrease the statistical efficiency of treatment comparisons. This is mainly because a study with too many clinical centers usually includes quite a few small centers and very often they do not have enough patients to represent all treatment groups. These small centers often carry little information on treatment differences. This paper utilizes a statistical model to quanttfy the relationship between statistical efficiency and the number of centers under typical clinical trial settings. Results in this paper provide useful statistical knowledge in choosing the number of clinical centers when planning multicenter studies. Key Words: Clinical trial; Multicenter; Number of clinical centers; Center size; Statistical power
INTRODUCTION IN THE PHARMACEUTICAL industry it is often important to ensure fast patient enrollment. A common practice to speed up patient enrollment is to use more clinical centers. One concern about this practice is whether there is any statistical penalty associated with the increase of the total number of study centers. What needs to be answered is how many study centers we can use in a clinical study without losing statistical efficiency. Actually, there is no simple and general answer that is appropriate for all studies, because it depends on many aspects of the
Reprint address: Zhengning Lin, Senior Biostatistician, Medical Information Processing and Statistics, Novartis Pharmaceuticals Corporation, 59 Route 10, East Hanover, NJ 07936. [email protected].
trial conduct at all study centers which may affect the study quality as more and more centers join the study. The approach in this paper focuses on the following statistical perspective: How much, if any, statistical efficiency is affected by the increase of study centers, while the study conduct and the overall quality of study centers remains unchanged? I use a statistical model to quantify the relationship between the number of centers and the statistical efficiency under typical clinical trial settings. Statistical efficiency is discussed in terms of actual statistical power. Results in this paper provide useful statistical knowledge regarding how many centers we may use when planning a multicenter clinical study. For simplicity of explanation, the discussion focuses on multicenter studies with the objective of comparing two treatments, while the conclusions ar
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