PEDIATRICS Vol. 107 No. 6 June 2001, pp. 1335-1342

Effects of Medicaid Managed Care on Quality: Childhood Immunizations

Evaline A. Alessandrini, MD, MSCE^*, Kathy N. Shaw, MD, MSCE^*, Warren B. Bilker, PhD, Donald F. Schwarz, MD, MPH, and Louis M. Bell, MD^{*, §}

From the Divisions of ^* Emergency Medicine,  Adolescent Medicine, and ^§ General Pediatrics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania; and  Department of Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania.

	ABSTRACT

Top Abstract Methods Results Discussion References

Background.  Underimmunization is distributed unevenly across populations, concentrated among the impoverished. Managed care has stimulated the development of quality indicators such as immunization rates to assess health status of populations.

Objective.  To determine if enrollment in Medicaid managed care (MMC) improves quality of health care as reflected by immunization rates when compared with fee-for-service Medicaid (FFSM).

Design.  Prospective cohort study of infants born between May 1994 and April 1995 with a 24-month follow-up period.

Setting.  Urban teaching hospital and surrounding ambulatory settings.

Participants.  Consecutive sample of infants (n = 644) enrolled in MMC or FFSM. Ninety-two percent of eligible patients were enrolled, and 87% completed follow-up.

Main Outcome Measure.  Up-to-date immunization status.

Results.  Seventy-three percent of the MMC and 72.4% of the FFSM patients were up-to-date on their immunizations: relative risk 1.01, (95% confidence interval [CI] 0.87, 1.17). No differences were found in age at immunization between the MMC and FFSM groups. After adjusting for other factors in multivariate analysis, insurance status remained unassociated with immunization status: adjusted odds ratio (OR) 1.04, (95% CI: 0.90, 1.10). Factors associated with up-to-date immunization included firstborn child, OR 2.28 (95% CI: 1.45, 3.60) and adequate maternal prenatal care, OR 2.24 (95% CI: 1.44, 3.48). Variables characterizing children less likely to be adequately immunized included father living in home with child, OR 0.53 (95% CI: 0.33, 0.85) and using private office-based primary care, OR 0.39 (95% CI: 0.23, 0.63).

Conclusions.  Enrollment in MMC did not improve rates of immunizations when compared with FFSM.  Key words:  Medicaid managed care, childhood immunization, quality.

Indigent children constitute a large proportion of the US population living below the poverty level. These children have limited access to health care and poor health status. Numerous studies have found that patients who are of lower socioeconomic status receive fewer medical services, particularly ambulatory care.^1-4 Other studies have suggested that poor patients have poorer health.^5,6 Taken together, these findings raise important concerns that deficits in care for disadvantaged groups may be at least partially responsible for their poorer health. Several studies have demonstrated a direct link between differences in health care use and health status between the disadvantaged and other populations.^7,8

Medicaid plays a critical role in providing health coverage for low-income children in the United States. In 1996, Medicaid paid for 4 of 10 births in the United States, and 21.3 million childrennearly one quarter of all US childrenwere enrolled in Medicaid for health care services.^9,10 Although a substantial body of literature demonstrates the effectiveness of having insurance and the importance of Medicaid in expanding health care for low-income children,^2,11,12 there is considerably less evidence to assess how the shift to managed care arrangements under Medicaid has influenced health care for poor children.

Although there are many reasons for the dearth of evidence on child health services delivery and outcomes after implementation of managed care, a contributing factor is that there are few valid, reliable, and easily implemented measures for assessing child health care outcomes. Immunization rates are valid and reliable markers of quality pediatric care. Rodewald and colleagues¹³ found that underimmunization was a powerful, independent marker for inadequate health supervision in an impoverished population.

Immunization rates are an area where coordinated care through a managed care plan could have a significant effect. Research has not shown that Medicaid managed care (MMC) programs have made a demonstrable improvement in the share of children being immunized. A 1985 evaluation of California and Missouri managed care demonstration programs found that immunization rates for children in MMC were comparable to those in fee-for-service arrangements and that the rates for children in both groups were low.¹⁴ A study of families in Los Angeles in 1992 again showed no difference in immunization status at 24 months of age between MMC and fee-for-service patients.¹⁵ Others have found, however, that low-income children enrolled in managed care had lower immunization rates than children in other arrangements.^16,17

We longitudinally followed a cohort of Medicaid enrolled infants for the first 24 months of life to determine if enrollment in MMC affected quality of care as measured by immunization rates and selected screening tests when compared with infants receiving fee-for-service Medicaid (FFSM). We hypothesized that enrollment in a MMC plan would improve the quality of health care delivered. In addition, this study assessed other factors that influenced up-to-date immunization status in this Medicaid population.

	METHODS

Top Abstract Methods Results Discussion References

Study Design and Participants

We performed a prospective cohort study of a consecutive sample of infants born between May 1994 and April 1995 at an urban, tertiary care center that provides primary obstetric care. Eligible newborns included those enrolled in FFSM or MMC with a birth weight 2 kg and gestational age 34 weeks. Newborns not discharged from the nursery within 10 days of birth were excluded, as were families in which no one in the home spoke English. In addition, mothers and their infants had to reside in 1 of 6 nearby zip codes. During the study time period, patients in 3 of these zip codes had mandated enrollment in MMC and patients in the remaining zip codes received FFSM health insurance. At the time of the study, this system of geographically determined mandated managed care had been in place for 8 years.

Five MMC plans provided insurance to study enrollees from 1994 to 1997. Two plans comprised 82% of managed care plans used by study participants. Physicians providing primary care to MMC patients during this time period acted as case managers and were capitated for primary care in all of the 5 MMC plans in which our patients were enrolled. However, practitioners were not at risk for overutilization of care, nor were there quality pools available to provide financial incentives for improved performance. During the study, immunizations were financed for all Medicaid-insured patients via the federal Vaccine for Children program. This program paid for and distributed free vaccine to providers via the Department of Public Health. To receive vaccine, providers needed only to send a letter to the Department of Public Health stating the number of patients in their practice and the proportion insured through Medicaid.

Measurement of Exposures

Information regarding insurance status was obtained via maternal postpartum interview, medical record review, and consultation with the maternity ward social worker. Mothers were also asked to show their Medicaid insurance card to study investigators at the time of enrollment. Other infant, maternal, and health care variables were also obtained from these sources. Three trained research nurses performed daily patient enrollment. Phone calls were made to study families 3 to 4 times during the 24-month follow-up period to verify residence, insurance status, and primary care physician (PCP).

Socioeconomic status indicators included cash assistance eligibility by self-report (individual level), as well as census tract data (neighborhood level)¹⁸ on median income and percentage below the poverty level for families with children. Adequate prenatal care was defined as initiation of care in the first trimester of pregnancy with 8 or more visits for a 34 to 35 weeks' gestation newborn and 9 or more prenatal visits for 36 weeks' gestation newborn.¹⁹ Characteristics of primary care offices and other health-care related variables were obtained by a survey mailed to PCP offices of participating study patients.

Outcomes

A trained research assistant, who did not perform patient enrollment and was blinded to the main study hypothesis, obtained outcome data by reviewing all physician office records for ambulatory patient encounters where an immunization or health screening test occurred. Compliance with recommended screening tests was assessed by the proportion of patients who had received tuberculosis and lead screening, and patient age at the time of these tests.

Immunization status was calculated as a dichotomous measure at 24 months old. Up-to-date immunization status was defined as 4 diphtheria-tetanus-pertussis vaccines (DTP), 3 poliomyelitis vaccines (PV), 4 Haemophilus influenzae type b (Hib) vaccines, 3 hepatitis B vaccines (HBV), and 1 measles, mumps, and rubella vaccine (MMR).²⁰ Delayed immunization status was thus defined as omission of any 1 or more of the above listed vaccines at 24 months old. Patient age at administration of DTP 1, DTP 4, and MMR were also calculated in months.

Data Analysis

Based on national and regional data of immunization status of US infants in 1994, we assumed that 65% of infants enrolled in FFSM would be up to date in their immunizations at 24 months old.^21-23 Anticipating that ~500 patients of the approximately 600 patients available for inclusion would complete the 24-month follow-up period, we had 80% power to detect a 25% relative improvement in immunization rates for the MMC group.

For comparing 2 groups, differences for continuous variables were assessed by t tests, or by the Mann-Whitney statistic if normality could not be assumed. The Kruskall-Wallis test was used for comparing the medians of 3 groups. ² tests and relative risk with 95% confidence intervals (CIs) were determined for dichotomous exposure and outcome variables. The Fisher's exact test was used if an expected cell value was <5. All statistical tests were 2-tailed with a 5% level of significance.

Multiple logistic regression was used to explore the relationship between the exposure variables and immunization status. Initially, unadjusted odds ratios (ORs) were used to assess the relationship between each independent variable and immunization status (up-to-date or not up-to-date). Variables with a P value <.2 were chosen for inclusion as potential predictors in a stepwise logistic regression analysis. The risk of developing the outcome, adjusting simultaneously for all other predictors included in the logistic regression model, are presented as adjusted ORs with 95% CIs.

The institutional review boards of the participating hospitals and the Philadelphia Department of Public Health approved this study. Written informed consent was obtained for all participants.

	RESULTS

Top Abstract Methods Results Discussion References

Cohort Characteristics

Ninety-two percent of 644 eligible infants were enrolled in the study. Thirty-three (5%) refused study participation and 20 (3%) mothers were unavailable to participate because of complications or procedures after delivery. Twenty-four-month follow-up was completed on 87% of enrolled patients (Fig 1). Fifteen percent of patients were enrolled in FFSM (n = 76), and 85% were enrolled in MMC (n = 437). There were no differences between patients completing follow-up and those not enrolled or lost to follow-up with regard to type of Medicaid, zip code of residence, gestational age, birth weight, race, or maternal age. Two patients died during the follow-up period and 9 declined additional study participation. The remainder was lost because of inability to contact this highly mobile population or loss of Medicaid eligibility.

View larger version (19K): [in this window] [in a new window]   Fig. 1.   Patient participation summary.

The MMC and FFSM groups were very similar with regard to the infant and maternal characteristics studied (Tables 1 and 2). The only differences found were that mothers of MMC patients were more likely to be born in the United States and report cash assistance eligibility.

Neighborhood level socioeconomic status indicators were collected by analysis of Philadelphia census tract data combined for eligible zip codes. Median income for families with children within these census tracts ranged from $19 724 to $31 286. The percentage of families with children living below the poverty level ranged from 17% to 51% with a mean of 31% and a standard deviation of 12.

Approximately 85% of all infants' mothers identified a PCP at the time of study enrollment; however, only a minimal proportion had scheduled a visit before the infant's nursery discharge (Table 1). Two hundred fifty-six infants (50%) attended a hospital-based clinic for primary care. Eighty-nine percent of hospital-based care was provided at a Children's Hospital site. Forty-five percent of Children's Hospital care was provided onsite, and 55% was provided at a satellite clinic. One hundred fifty-six infants (30%) attended a Philadelphia Department of Public Health Clinic or a federally qualified health center. These sites are denoted as community clinics. The remaining 101 patients (20%) used a private doctor's office as their site of primary care. Although there was no difference in the proportion of MMC or FFSM patients using hospital-based or community clinics; MMC patients (21%) were nearly twice as likely as their FFSM counterparts (11%) to attend a private doctor's office for primary care (P = .04).

Ninety-eight percent (46/47) of primary care offices responded to a mailed survey inquiring about office attributes. These offices provided a mean of 37.2 (± 8.6) hours of weekday daytime office hours, 2.6 (± 3.8) hours of weekday evening hours, and 1.6 (±2.4) hours of weekend office hours each week. There were no differences between these office attributes for patients with MMC and FFSM.

Immunization and Screening Test Status

Enrollment in MMC did not improve immunization rates at 24 months of age. Overall, 72.9% (n = 374) of our population was adequately immunized. There was no difference between the FFSM (73.0%) and MMC (72.4%) groups at the end of the study period: relative risk 1.01, (95% CI: 0.87, 1.17; Table 3). Exclusion of the hepatitis B vaccine series did not alter up-to-date immunization status in this patient population.

We also evaluated the proportion and age of patients receiving selected immunizations and preventive screening evaluations (Fig 2A and B). Virtually all study patients received their first DTP during the follow-up period. Approximately 90% of patients received a measles-containing vaccine and lead screening. Approximately 80% received their fourth DTP and a tuberculosis screen. These immunizations and screening tests were performed in a timely fashion as recommended by the American Academy of Pediatrics.²⁰ There were no differences between MMC and FFSM in any of these measured parameters.

View larger version (32K): [in this window] [in a new window]   Fig. 2.   A) Immunization status and screening tests by Medicaid insurance type at 24 months of age. B) Age at immunization or screening test by Medicaid insurance type.

Differences in measures of quality were noted by site of primary care (Fig 3). The most notable difference was found among primary care sites with regard to proportion of patients achieving up-to-date immunization status at 24 months of age. Whereas 80% of hospital-based children and 74% of community clinic patients were up-to-date, only 55% of patients followed by a private physician's office had completed the recommended immunization series (P < .0001 and P = .002 for comparison with hospital and community clinics, respectively). Only receipt of DTP 1 did not differ between primary care sites, occurring in >97% of each group. All immunizations and screening tests were performed at a later age at the private office sites when compared with the hospital and community clinic sites.

View larger version (47K): [in this window] [in a new window]   Fig. 3.   A) Immunization status and screening tests by primary care site at 24 months of age. B) Age at immunization or screening test by primary care site.

Factors Associated With Up-to-Date Immunizations

Nine independent variables were identified as being associated with immunization status at 24 months old. Factors associated with up-to-date immunizations included first-born child (OR: 2.71), child living in home with mother and maternal grandmother (OR: 1.36), and adequate maternal prenatal care (OR: 2.41). Variables characterizing children less likely to be adequately immunized included male gender (OR: 0.68), father living in home with child (OR: 0.49), cash assistance eligibility (OR: 0.70), teenage mother (OR: 0.96), having a family car (OR: 0.64), and private office-based primary care (OR: 0.35).

After adjusting for these infant, maternal, and health care variables in multivariate analysis, insurance status remained unassociated with up-to-date immunization statusadjusted OR: 1.04 (95% CI: 0.90, 1.10). Multivariate analysis revealed several factors associated with immunization status (Table 4), including first-born child, adequate maternal prenatal care, father living in home with child, and having a private office-based primary care site.

	DISCUSSION

Top Abstract Methods Results Discussion References

Our prospective cohort study found no difference between patients enrolled in MMC and those enrolled in FFSM with regard to the quality indicators of immunization status or health screening tests. As experience with MMC has been accumulating during the past 15 years, we must continue to assess its role in quality and outcomes to understand its impact on the health of the people that the program serves.

Our definition of up-to-date immunization status is more stringent than the so-called 4:3:1 series often used as an immunization outcome measure for children at 24 months of age. The 4:3:1 series includes 4 DTP, 3 PV, and 1 MMR. We elected to include 3 HBV and 4 Hib vaccines in our definition, as both vaccines were included in the 1994 American Academy of Pediatrics/Advisory Committee on Immunization Practices recommended immunization schedule²⁰ and both diseases are clinically important to prevent.

The 73% up-to-date immunization rate found in this study was higher than anticipated based on national and regional data of urban children available in 1994.^21-23 Of note, the 1997 National Immunization Survey found that for non-Hispanic blacks living below the poverty threshold, 72% of children 19 to 35 months old were complete for the 4:3:1 series.²⁴ During this time period, improved vaccine delivery may have been aided by the federal Vaccine for Children program, part of the 1993 Childhood Immunization Initiative, which pays for and distributes free vaccine to providers,²⁵ and the discovery of low immunization rates among urban children during the recent measles epidemic.²⁶

Two previous studies, whose primary goal was to investigate the influence of MMC on infant immunizations, also found no difference between MMC and FFSM in the percentage of children who were adequately vaccinated.^14,15 The first study, performed at the initiation of the Medicaid competition demonstrations, evaluated 2735 children's charts in mandated managed care and fee-for-service counties for health care received in 1985. Up-to-date immunization status (3 DTP and 3 PV at 1 year of age) ranged from 57% to 70% in the various counties studied. In multivariate analysis, demonstration counties performed slightly better than their fee-for-service counterparts, although the ORs reflecting increased likelihood (1.05-1.08) were modest but important.¹⁴ However, because immunizations were only abstracted from 1 PCP site per patient, and there was a higher abstraction rate in the MMC group, it is possible that the immunization rate in the FFSM group was underestimated. In our study, we were able to record data from all sites at which an immunization or screening test was provided for both MMC and FFSM patients.

In the second study, immunization status at 24 months old was assessed for 430 patients using hand-held immunization records and PCP records if hand-held records were not available. No difference in up-to-date immunization status (4:3:1) was found by type of insurance in either univariate or multivariate analysis. Up-to-date immunization status ranged from 34% in the MMC group to 45% in the FFSM group.¹⁵

Together with our study, these 3 studies span over a dozen years of MMC experience, and demonstrate no differences in immunization status despite using different sampling and research methods, different patient populations of different racial backgrounds and geographic locales, and different definitions of up-to-date immunization status. In our community, the MMC companies implemented several activities to enhance coordinated care and improved immunization levels. This included participation in a computerized immunization database with the Philadelphia Department of Public Health and chart audits for quality indicators, such as those used by Health Plan Employer Data and Information Set. Furthermore, several of the larger plans gave incentives, such as diapers and infant formula, to parents of children who were adequately immunized. In addition to lack of improved immunization rates, no changes in prenatal care or birth outcomes have been detected between patients enrolled in MMC and those in FFSM.²⁷ This indicates that these programs, now serving >13 million beneficiaries,²⁸ have not experienced the improvements expected from enrollment in a managed care system.

Despite the known efficacy of most pediatric vaccines, children in the United States continue to be inadequately immunized. Although type of Medicaid insurance does not seem to be related, multiple other factors have been associated with inadequate childhood immunization status. The 1988 National Maternal and Infant Health Survey of the National Center for Health Statistics served as the basis for a study that found that less formal maternal education, single marital status, maternal age <20 years, and higher birth order were related to underimmunization.²⁹ Other studies have consistently confirmed and expanded factors associated with undervaccination. These include higher birth order,^1730-32 younger maternal age,^30,33 less formal maternal education,³⁰ maternal single marital status,³⁴ lack of an identified primary care provider,³² and not living with a grandmother.³⁴ Previous studies also suggest that the pattern of maternal health care utilization, specifically prenatal care, is one of the most important determinants of immunization status and other pediatric health care utilization.^1733-34 The association of many of these factors with adequate immunization is corroborated both qualitatively and quantitatively in our research.

Infants who received well-child care at a private doctor's office were significantly less likely to be up-to-date on immunizations at 24 months old and less likely to have received lead screening. Wood's investigation of the impact of managed care on immunizations also found an association between site of medical care and up-to-date immunization status. In a multivariate analysis, they found that private offices were 43% as likely and prepaid health maintenance organizations 24% as likely as public health clinics to adequately immunize children by 24 months old. There was no difference between hospital-based sites and public health clinics.¹⁵ Several factors may explain the poor performance by the private sector in the inner city. Private practitioners may have financial disincentives, such as poor reimbursement rates, to provide immunizations. Although vaccines were available through the Vaccine for Children program to all practitioners during our study period, small offices may not comply with the necessary paperwork to receive free vaccine. In addition, missed opportunities to vaccinate children presenting for well-child or sick services may be very common in the private sector.¹⁷

The Institute of Medicine defines quality as "the degree to which health services for individuals and populations increase the likelihood of desired health outcomes".³⁵ Immunization status is an outcome measure to evaluate quality of care already used by physicians and health insurance companies. A recent study of all 34 states with comprehensive prepaid managed care contracts in 1996 found that 25 (83%) of 30 states that responded collected data on childhood immunization rates in 1995 to 1996. However, only 9 of 30 state Medicaid agencies surveyed provided comparative information on childhood immunizations to health plans, and no states offered this information to Medicaid beneficiaries in the process of selecting managed care plans.³⁶

Strengths of this study included an excellent follow-up rate, outcome measures that were accurately and comprehensively obtained via medical record review, and comparison groups that were similar with respect to important determinants of immunization status other than type of Medicaid insurance. However, there were also several limitations. Our sample size was limited to expanding the follow-up on an existing cohort, consequently our detectable difference in immunization status of 25% may be considered too large by others involved in immunization-related research. However, reviewing the 95% CIs around our relative risk, we would have been able to detect smaller and clinically important differences between MMC and FFSM patients' immunizaiton status had they existed. In addition, more MMC patients were enrolled in the study than FFSM patients. Although the enrolling hospital is located on the periphery of a mandated managed care zip code, it is geographically equidistant from MMC and FFSM areas of the city. We do not believe there is selection bias in that there were no significant differences in sociodemographic factors, patients refusing study participation, or those lost to follow-up by type of Medicaid insurance. Finally, the generalizability of this urban cohort is limited to other large US cities with a tertiary care pediatric center.

In the future, the proportion of Medicaid-eligible children enrolled in managed care will likely increase as a result of recent legislation that relaxed the requirement that states seek federal approval before mandating managed care enrollment for Medicaid beneficiaries. As mandatory managed care enrollment for Medicaid recipients increases nationwide, changes in quality and implications for the delivery of pediatric health services and health outcomes must be monitored. Continued vigilance across all aspects of the health care system is necessary to ensure that quality health care is provided to children and their families.

	ACKNOWLEDGMENTS

This study was supported by The Pew Charitable Trusts, the Ambulatory Pediatric Association Immunizations Special Projects Program, and Public Health Services Research Grant MDI-RR00040 from the National Institutes of Health (Clinical Research Center, University of Pennsylvania).

	FOOTNOTES

Received for publication Jun 15, 2000; accepted Sep 27, 2000.

Address correspondence to Evaline A. Alessandrini, MD, MSCE, Division of Emergency Medicine, Children's Hospital of Philadelphia, 34th St and Civic Center Blvd, Philadelphia, PA 19104. E-mail: alessandrini{at}email.chop.edu

	ABBREVIATIONS

MMC, Medicaid managed care; FFSM, fee-for-service managed care; PCP, primary care physician; DTP, diphtheria-tetanus-pertussis; PV, poliomyelitis; HIB, Haemophilus influenzae type b; HBV, hepatitis B vaccine; MMR, measles, mumps, and rubella; CI, confidence interval; OR, odds ratio.

	REFERENCES

Top Abstract Methods Results Discussion References

1. Newacheck PW, Halfon N Preventive care use by school-aged children: differences by socioeconomic status. Pediatrics. 1979; 64:304-309 [Abstract/Free Full Text]
2. Newacheck PW, Halfon N Access to ambulatory care services for economically disadvantaged children. Pediatrics. 1986; 78:813-819 [Abstract/Free Full Text]
3. Newacheck PW, Hughes DC, Stoddard JJ Children's access to primary care: differences by race, income, and insurance status. Pediatrics. 1996; 97:26-32 [Abstract/Free Full Text]
4. Stoddard JJ, St Peter RF, Newacheck PW Health insurance status and ambulatory care for children. N Engl J Med. 1994; 330:1421-1425 [Abstract/Free Full Text]
5. Freeman HE, Blendon RJ, Aiken LH, Sudman S, Mullinix CF, Corey CR Americans report on their access to health care. Health Aff (Millwood). 1987; 6:6-8 [CrossRef][Medline]
6. Rowland D, Lyons B Triple jeopardy: rural, poor and uninsured. Health Serv Res. 1989; 23:975-1004 [Medline]
7. Bindman AB, Keane D, Lurie N A public hospital closes: impact on patients' access to care and health status. JAMA. 1990; 264:2899-2904 [Abstract/Free Full Text]
8. Lurie N, Ward NB, Shapiro MF, Gallego C, Vaghaiwalla R, Brook RH Termination of Medi-Cal benefits: a follow-up study one year later. N Engl J Med. 1986; 314:1266-1268 [Medline]
9. National Governors Association (US). MCH Update: State Medicaid Coverage of Pregnant Women and Children. Washington, DC: National Governors Association (US); 1997
10. Holahan J, Bruen B, Liska D. The Decline in Medicaid Spending Growth in 1996: Why Did it Happen? Washington, DC: Kaiser Commission on Medicaid Uninsured; 1998
11. Davis K, Rowland D. Financing Health Care for the Poor. Cambridge, MA: Harvard University Press; 1991
12. Wilson RW, White EL. Changes in morbidity, disability, and utilization differentials between the poor and the non-poor: data from the health interview survey 1964 and 1973. Med Care. 1977:15:636-646
13. Rodewald LE, Szilagyi PG, Shiuh T, Humiston SG, LeBaron C, Hall CB Is under-immunization a marker for insufficient utilization of preventive and primary care? Arch Pediatr Adolesc Med 1995; 149:393-397 [Abstract/Free Full Text]
14. Carey T, Weis K, Homer C Prepaid versus traditional Medicaid plans: effects on preventive health care. J Clin Epidemiol 1990; 43:1213-1220 [CrossRef][Medline]
15. Wood D, Halfon N, Sherbourne C, Grabowsky M Access to infant immunizations for poor, inner-city families: what is the impact of managed care? J Health Care Poor Underserved 1994; 5:112-123 [Medline]
16. Lieu TA, Smith MD, Newacheck PW, Langthorn D, Venkatesh P, Herradora R Health insurance and preventive care sources of children at public immunization clinics. Pediatrics 1994; 93:373-378 [Abstract/Free Full Text]
17. Wood D, Donald-Sherbourne C, Halfon N, Factors related to immunization status among inner-city Latino and African-American preschoolers. Pediatrics 1995; 96:295-301 [Abstract/Free Full Text]
18. Brook RH, Kamberg CJ, Lohr KN, Quality of ambulatory care: epidemiology and comparison by insurance status and income. Med Care 1990; 28:392-433 [Medline]
19. Kotelchuck M. Overview of prenatal care utilization index [mimeo]. Chapel Hill, NC: School of Public Health, University of North Carolina; 1987
20. American Academy of Pediatrics. In Peter G, ed. Red Book: Report of the Committee on Infectious Diseases. 23rd ed. Elk Grove Village, IL: American Academy of Pediatrics; 1994
21. Cutts FT, Zell ER, Mason D, Bernier RH, Dini EF, Orenstein WA Monitoring progress toward US preschool immunization goals [review]. JAMA 1992; 267:1952-1955 [Abstract/Free Full Text]
22. Centers for Disease Control Retrospective assessment of vaccination coverage among school-aged childrenselected US cities, 1991. MMWR Morb Mortal Wkly Rep. 1992; 41:103-107 [Medline]
23. Centers for Disease Control and Prevention State and national vaccination coverage levels among children age 19-35 monthsUnited States. MMWR Morb Mortal Wkly Rep 1994; 44:613-622
24. Centers for Disease Control and Prevention National, state, and urban area vaccination coverage levels among children aged 19-35 monthsUnited States, July 1996-June 1997. MMWR Morb Mortal Wkly Rep 1998; 47:108-116 [Medline]
25. Wood DL, Halfon N The impact of the vaccine for children's program on child immunization delivery: a policy analysis. Arch Pediatr Adolesc Med 1996; 150:577-581 [Abstract/Free Full Text]
26. Centers for Disease Control and Prevention MeaslesUnited States. MMWR Morb Mortal Wkly Rep. 1993; 42:378-381 [Medline]
27. Goldfarb NI, Hillman AL, Eisenberg JM, Kelley MA, Dohen AV, Dellheim M Impact of Medicaid mandatory case management program on prenatal care and birth outcomes. Med Care 1991; 29:64-71 [CrossRef][Medline]
28. Health Care Financing Administration. Medicaid managed care state enrollment. Health Care Financing Administration; 1997. Available at: http://www.hcfa.gov/medicaid/plantyp7.htm. Accessed February 2000
29. Mustin HD, Holt VL, Connell FA, Adequacy of well-child care and immunizations in US infants born in 1988. JAMA 1994; 272:1111-1115 [Abstract/Free Full Text]
30. Moore P, Fenlon N, Hepworth JT Indicators of differences in immunization rates of Mexican American and white non-Hispanic infants in a Medicaid managed care system. Public Health Nurs 1996; 13:21-30 [Medline]
31. Griffin MR, Daugherty J, Reed GW, Immunization coverage among infants enrolled in the Tennessee Medicaid program. Arch Pediatr Adolesc Med 1995; 140:559-564
32. Lieu TA, Black SB, Ray P, Risk factors for delayed immunization among children in an HMO. Am J Public Health 1994; 84:1621-1625 [Abstract/Free Full Text]
33. Stevens-Simon C, Kelly LS, Singer D Pattern of prenatal care and infant immunization status in a comprehensive adolescent-oriented maternity program. Arch Pediatr Adolesc Med 1996; 150:829-833 [Abstract/Free Full Text]
34. Bates AS, Fitzgerald JF, Dittus RS, Risk factors for underimmunization in poor urban infants. JAMA 1994; 272:1105-1115 [Abstract/Free Full Text]
35. Institute of Medicine. Medicare: A Strategy for Quality Assurance. Vol 1. Washington, DC: National Academy Press; 1990
36. Landon BE, Tobias C, Epstein AM Quality management by state Medicaid agencies converting to managed care: plans and current practice. JAMA 1999; 279:211-216 [Abstract/Free Full Text]