In addition to the reasons listed by other commenters, my feeling that it is also just a matter of the trial results being delayed. This can happen for a numbe

In addition to the reasons listed by other commenters, my feeling that it is also just a matter of the trial results being delayed. This can happen for a number of reasons. * Insufficient patients are not willing to consent to enroll in the trial. This is usually solved simply by extending the duration of the study * Doctors are to busy to obtain informed consent from patients, and take the easier path of not mentioning that they qualify for a trial. This happens often in hospitals that join a trial but are not directly research oriented. * Delay in the data-collection, statistical analysis or interpretation of the results. As in other fields, statisticians are constantly kept busy, and often change profession. Lack of personnel can delay the result of the trial.