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.
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.