[1] BETH ISRAEL HOSP, DEPT MED, BOSTON, MA 02215 USA
[2] HARVARD UNIV, SCH MED, THORNDIKE MEM LAB, BOSTON, MA 02115 USA
[3] HARVARD UNIV, SCH MED, CTR ANAL HLTH PRACTICES, BOSTON, MA 02115 USA
[4] GEORGE WILLIAMS HOOPER FDN, SAN FRANCISCO, CA USA
[5] UNIV CALIF SAN FRANCISCO, MED CTR, SAN FRANCISCO, CA 94143 USA