1. Departments of Pediatrics (K.W.-P., R.C.P., B.G., I.B.S.), David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California 90095
2. Biomathematics (H.W., R.M.E.), David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California 90095
3. Department of Pediatrics (S.S.), Loma Linda University, Loma Linda, California 92354
4. Department of Pediatrics (H.J.), Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02115