Pring CM, Skelding-Millar L, Goodall RJ. Expectant treatment or cholecystectomy after endoscopic retrograde cholangiopancreatography for choledocholithiasis in patients over 80 years old? Surg Endosc. 2005 Mar;19(3):357-60.
Williams VSL, Wakeford ME. The predictive validity of the National Teacher Examinations for performance in teacher education programs. Educ Psychol Meas. 1993;53(2):533-9. doi: 10.1177/0013164493053002023