It turns out that evaluation by the flight instructor at the time of solo (typically at eight hours of dual) was the most efficient predictor of a student's success at passing the checkride. The biographical inventory and the interview were the next best predictor of a student's success. This shouldn't come as a surprise to any instructor. Most CFIs can get a good feel for someone's ability to fly by learning about them, then spending a few hours in the cockpit seeing how they handle an airplane.
On the other hand, the flight examiner's evaluation on the final flight test showed "low correlations with instructors' ratings of students at the end of the course and with ratings by a check pilot at the completion of the course." The report said, "The data raise doubts as to the value of the CAA Flight Test which now require so much time and energy on part of the inspectors...."
Have you ever wondered why a student's checkride examination may not always correlate with an instructor's and phase check pilot's pre-checkride evaluation of that student? Apparently early educational researchers wondered about this, too. On the other hand, this study provides justification for flight schools that forego final flight checks in favor of progressive phase inspections.