The participant and control groups’ mean age, proportion disabled, proportion dying annually, average number of comorbidities, and prevalence of each comorbidity were similar at baseline (eTable 2
). Control group beneficiaries were slightly more likely to be women, Medicaid eligible, and black. Demographics of the participant and control groups did not change appreciably between the preintervention and postintervention periods, suggesting PGPD participants did not systematically target specific demographic groups for either enrollment or disenrollment.
The depicts unadjusted annual means of spending in each year for beneficiaries assigned to PGPD physician groups and local controls. This illustrates that trends in the participants and controls were similar in the pre-PGPD period. The also illustrates that for all enrollees, the reduction in growth of spending for non-dually eligible beneficiaries was modest. Overall, average annual Medicare payments per beneficiary in PGPD participating sites increased by $1206 (15.2%) between the preintervention and postintervention periods and $1230 (16.5%) for controls. After adjustment, per capita annual savings estimates were modest ($114, 95% CI, $12–$216, P =.03, ) (full regression results are available upon request). This result reflects the average of significant annual savings in the dually eligible beneficiaries ($532, 95% CI, $277–$786, P < .001) and nonsignificant savings in the nondually eligible beneficiaries ($59, 95% CI, $166 in savings to $47 in additional spending, P =.28).
Medicare Spending per Beneficiary: Physician Group Practice Demonstration Participants and Local Controls
Savings estimates were sensitive to the approach to risk adjustment used. These analyses are presented in . The true per beneficiary savings attributable to the PGPD therefore are likely to lie between the conservative mean LVC-adjusted result ($114) and the mean HCC-adjusted result ($496, 95% CI, $468–$524, ), which may be more susceptible to coding biases.11
Changes in participant and control group health status during the study period differed depending on the measurement method used. The baseline mean HCC score was 1.05 for PGPD participants and 1.03 for the local controls (eTable 2
). Mean HCC scores increased to 1.18 for PGPD participants, a 12.4% increase, and to 1.12 for controls, an 8.7% increase. After regression adjustment, we found a significant positive association between PGPD participation and mean HCC score changes over time (0.03 increase in HCC score during the intervention period, 95% CI, 0.029–0.32, P
< .001). The differential changes in HCC score were not mirrored in measures of risk less susceptible to potential manipulation such as age or mortality rates, which both went down during the intervention period.
Across participating systems, estimated savings and the effect of risk adjustment approaches varied markedly, with mean LVC-adjusted estimates ranging from savings of $866 annually per beneficiary at the University of Michigan (95% CI, $815–$918) to greater expenditures by $749 (95% CI, $698–$799) relative to controls at Middlesex (). Only 4 sites saved a significant amount across all beneficiaries (University of Michigan, Marshfield, Billings, and Forsyth), whereas 3 sites had no significant change and 3 sites increased expenditures relative to controls during the PGPD. Dartmouth-Hitchcock and Geisinger only exhibited savings under the HCC risk-adjustment approach; both had relatively large increases in HCC scores relative to their control group ().
Models stratified by the type of service demonstrate that significant savings occurred across all patients in acute care ($118, 95% CI, $65–$170) and home health care ($17, 95% CI, $7–$28, ). Further, analysis revealed that in sites where savings occurred on acute care, hospitalization rates declined during the PGPD.
Spending Changes Associated With Physician Group Practice Demonstration by Spending Categorya
The illustrates unadjusted growth in Medicare spending separated for dually eligible and nondually eligible beneficiaries. Within the dual beneficiary population, the rate of growth was similar in the intervention and control groups before the intervention. Between the preintervention and postintervention periods, the spending growth rate for dual beneficiaries treated by PGPD participants was 9.7% compared with a 15.3% increase among those treated by local control practices. As noted, this translates into mean $532 in annual per beneficiary savings in the dually eligible beneficiaries (95% CI, $277–$786, P < .001, ), or a 5% decrease in Medicare spending for the dually eligible patient. Savings in the dually eligible were less sensitive to the risk-adjustment approach ().
Much of these mean savings were achieved through a reduction in acute care hospitalizations ($381, 95% CI, $247–$515, ), procedures ($55, 95% CI, $15–$94), and home health care ($28, 95% CI, $64 in savings to $8 in additional spending). The reductions in spending were roughly similar across diagnosis groups, suggesting that savings may have been achieved through better care management overall rather than through disease-specific interventions.
The proportion of the assigned patient population that was dually eligible ranged from 11% in Billings and Middlesex to 20% in Forsyth, with a mean of 15% across all sites. Annual baseline spending on dually eligible beneficiaries ranged from $8739 in Marshfield Clinic to $17 511 in the University of Michigan Faculty Group Practice (). These 2 sites achieved substantial mean savings in the dually eligible beneficiaries (Marshfield, $987, 95% CI, $765– $1209 or 11%, University of Michigan, $2499, 95% CI, $2371–$2627 or 14%). Park Nicollet achieved substantial savings in the dually eligible beneficiaries ($1610, 95% CI, $1512–$1708) but also experienced increased spending in the nondually eligible ($188, 95% CI, $114–$262) and so on average did not produce savings.
There was no overall association between the PGPD and the probability of ED visits in either the full PGPD population or among dually eligible beneficiaries (). These averages, however, mask significant reductions in ED visits in the sites that produced the largest savings in dually eligible beneficiaries, Marshfield, Park Nicollet, and the University of Michigan. The PGPD was associated with lower medical 30-day readmissions on average across the 10 sites and lower readmissions for both medical and surgical admissions in the dually eligible beneficiaries ( and eTable 4
Changes in Utilization-Based Quality Measures Associated With the Physician Group Practice Demonstrationa,b