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P4P Improved Child Immunization Rates

Pay-for-performance can alter physician behavior if structured with appropriate and large enough incentives. This study based in New York showed that a P4P intervention can improve immunizations in children.

This study used a case-comparison and an interrupted time series design to compare Hudson Health Plan’s Pay for Performance (P4P) program — an intervention to improve immunization rates of children 0-2-years-old.  The interrupted time series allowed Hudson Health Plan to observe trends in immunization rates of its own patients and those covered by other plans before and after the implementation of the P4P program.  This study design sought to account for secular trends that might have confounded immunization rates for patients in the intervention population.

From 2003-2007, Hudson Health Plan, a not-for-profit Medicaid managed care plan out of New York, introduced a piece-rate P4P program offering financial incentives at the physician practice level to improve immunization rates for 4,429 eligible two-year-old children.  Hudson health plan contracts with 115 eligible practices. Sixty-five percent of the practices are solo or small.  Thirty-five percent are medium (4-9 physicians) or large practices (10 or more physicians).  The intervention was two tiered, offering $100 for each child fully immunized by their second birthday and an additional $100 if the immunizations were administered in compliance with Health plan Employer Data and Information Set’s (HEDIS) 2003 guidelines for timeliness.

Additionally, the program provided administrative support by providing monthly lists of patients turning two in the previous month, and quarterly reports on each practices immunization rates.  The principle findings show Hudson Health Plan immunization rates increasing at a moderate (7 percent from 2003-2005; 11 percent from 2005-2007) yet statistically significant higher rate than trends observed in comparison health plans.  The mechanisms by which this improvement took place remain unclear.  Examination of patient-level claims data showed no significant change in number of visits, number of shots per visit, immunization rates, or preexisting conditions.   Concerns over the program’s negative impact on children with chronic conditions or the exacerbation of racial/ethnic disparities did not come to fruition.

Two major limitations discussed by the authors of this study and those similar are an inability to account for secular trends at the patient or practice level that may affect immunization rates. The other limitations are an inability to differentiate between improved documentation and more complete immunizations in the intervention population possibly due to system gaming.


Many P4P programs are able to demonstrate improvements in incentivized behaviors.  The fundamental basis of program success remains a topic for further research.   In this era of healthcare quality improvement, secular trends geared toward educating patients and providers, increasing use of quality measures, improved reporting of quality indicators, movements toward evidence-based practice, and payment system reforms exist as confounders skewing the evaluation of P4P programs.  The authors attempted to account for this potential confounding using a study design allowing for comparison of immunization rates of children in and out of Hudson Medicaid health plans before P4P implementation and post intervention.  Hudson’s immunization trends were significantly improved compared to those of non-Hudson plans.

The potential for system gaming in P4P programs (i.e. improved documentation of incentivized behaviors versus actual improvement in behaviors; denial of care for sicker patients to achieve incentivized standards), requires further investigation.

Chien, AT, Li, Z, and Rosenthal, MB. “Improving timely childhood immunizations through Pay for Performance in Medicaid-Managed care.”  HSR. 2010 Dec; 45 (6 Pt 2):1934-47.


Patrick Fitzgerald, MPH

Patrick Fitzgerald, MPH
About Patrick Fitzgerald, MPH

Mr. Fitzgerald currently works as an analyst for UCare, a Managed Care Organization serving Medicaid and Medicare recipients in Minnesota and western Wisconsin. Contact: Facebook | More Posts

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