Fady,
I do agree with your statement that with multi-center studies, there is a greater chance for variability within the studies. In order to reduce variability, it is important to have the same internal staff throughout the study with proper training. This would assist in having a consistent set of data collection and analysis. In addition, having the ability to provide the SOP that needs to be followed through the study and making sure that is the case with every center. Furthermore, there is a chance that variability can come from the population chosen at random and how they can be affected differently with the device. And this may be why most companies would like to expand the number of centers to cover the population difference. So it’s a bit tough to say that a certain number of centers is enough. The line should be drawn at the point that you don’t have enough staff to run the study consistently and it still helps to maintain a quality clinical trial.