Methodological issues in determining rates of childhood immunization in office practice - A study from pediatric research in office settings (PROS)

Objective: To compare 3 methods for measuring pediatric office immunization rates. Design: Retrospective and prospective cross-sectional surveys. Patients: Children 2 and 3 years old from 15 pediatric practices in 11 states. Methods: Immunization rates were determined for each practice using 3 methods. The Consecutive method used data from the practice's medical records of patients seen consecutively in the office; the Chart method used data from randomly selected practice medical records; and the Active method (reference standard) used a combination of medical record data with a telephone interview to collect additional immunization data and current patient status, using data only on current patients. Analyses were based on a mean of 57, 62, and 51 (Consecutive, Chart, and Active method, respectively) patients per practice. Patients were considered fully immunized if they had received 4 doses of DTP/DT vaccine, 3 doses of OPV/IPV, and 1 dose of MMR vaccine by their second birthday. Comparisons were made using the paired t test. Results: The mean immunization rate by method was Consecutive, 81.5% (range, 51%-97%); Chart, 71.6% (range, 42%-94%); and Active, 79.6% (range, 53%-96%). Within a given practice, the differences between methods varied considerably (0 to 28 percentage points). The mean difference from the reference standard Active method was 8 percentage points (P<.001) for the Chart method and -1.9 percentage points (P=.36) for the Consecutive method. The largest difference was between the Consecutive and Chart methods (mean difference, 9.9 percentage points; P=.003). Practitioners uniformly found the Consecutive method easiest to implement. Conclusions: Practice-specific immunization rates are one of the few objective measures of the quality of preventive pediatric care. Pediatric practices monitoring their immunization rates should consider using the Consecutive method, a simple, acceptable, and valid measure of practice immunization rate.