Statistical issues in interpreting clinical trials.

Randomized clinical trial is an important research tool in evaluating new therapeutic agents, devices and procedures. In order to obtain reliable and unbiased results, careful consideration must be given in the design and conduct of the trial. However, bias can be introduced in the analysis of the final data if certain principles are not followed. Several issues are described that make interpretation of analyses challenging. These include the intent-to-treat principle, the use of surrogate outcome measures, subgroup analyses, missing data and noninferiority trials.