1. Biostatistics Unit; Group Health Research Institute; Seattle WA USA
2. Department of Biostatistics; University of Washington; Seattle WA USA
3. Department of Population Medicine; Harvard Medical School and Harvard Pilgrim Health Care Institute; Boston MA USA
4. Kaiser Permanente Division of Research; Oakland CA USA
5. Department of Research and Evaluation; Kaiser Permanente Southern California; Pasadena CA USA
6. Immunization Safety Office; Centers for Disease Control and Prevention; Atlanta GA United States
7. Group Health Research Institute; Seattle WA USA