Monitoring of clinical trials. Establishment, measures and consequences

Background: Clinical trials play an important role in developing and establ ishing new therapeutic and diagnostic procedures. In the planning and execu tion of these trials procedures and measures which allow for continual obse rvation. description and evaluation of the study progress are to be taken i nto account. This is due to ethical, scientific and economic considerations . Together these procedures and measures are termed "monitoring" Repeated e valuation of the main study question is one particular monitoring measure. Results from this sequential procedure may lead to an early termination of patient recruitment. In the last 3 decades methods for interim analyses wer e developed which take into account the increased chance of errors when eva luating repeatedly the same question. By adjustment they guarantee a prespe cified level of significance in the end result of the trial. Even though statistical significance may be evident in an interim analysis, this has not always to result in early termination of the trial. The decis ion to end a trial early must include other considerations than the mere ev aluation of the main study question. In particular, consequences of the dec ision such as credibility and transferability of the trial result to subseq uent: therapeutic routine application are to be discussed.