The necessity of having a clinical background is highly dependent on the role you will have in the clinical trial. All of the roles will be made easier with some level of clinical experience, but they all can be conducted without it. Principal investigators and investigators will benefit immensely form this as they will be in the test center conducting the tests. That means they will be working with patients so and understanding of that dynamic and how working with patients can be will greatly increase their ability to conduct the trials. But for someone who will be doing the statistical analysis of the data the need for clinical experience will be minimal. If the study was designed well then the data will not need much interpreting, just simply taking the data and analyzing the trends to see if the test proved that the new treatment is statistically significantly more effective then the older treatment. In some ways having clinical experience could be a detraction as you may be tempted to look at the data as more than data, when it is important to be objective.