Figure 6. Graph shows the recruitment rate as a function of time since the start of the study. As long as the two strategies are considered equivalent, physicians will be comfortable with patients being randomly assigned to treatment. If, over time, it becomes clear from clinical experience that use of one of the diagnostic imaging strategies is preferable, physicians will be reluctant to recruit patients for the trial. Despite strict inclusion and exclusion criteria, a subtle change in those considered eligible for the trial may take place. A criterion for stopping the study (arrow) could be based on the percentage of potentially eligible patients recruited for the study.