Of the 132 physician groups included in the study, 79 (60%) were affiliated with a network, and 53 (40%) had no network affiliation (Table ). Approximately 59% of the physicians practiced in network-affiliated groups, but median number of PCPs per group was nearly twice as large in non-affiliated groups (26) as it was in network-affiliated groups (14). The study database included 860,589 measure opportunities across the 12 HEDIS measures we studied. Approximately 63% of measure opportunities occurred in network-affiliated groups. Each category of network affiliation and group size had an adequate number of measure opportunities for analysis.
Characteristics of Network-affiliated and Non-affiliated Physician Groups
Group size was weakly and inconsistently related to HEDIS performance scores. There were statistically significant differences in mean HEDIS performance rates between small, medium, and large physician group size categories for only 3 of the 12 HEDIS measures (monitoring diabetic nephropathy, acute phase antidepressant medication management, and continuation phase antidepressant medication management; Table ). Small groups had higher performance scores than others on these 3 measures.
Mean HEDIS Performance Scores by Physician Group Size Tercile
Network affiliation was associated with higher HEDIS performance scores. Patients of network-affiliated physician groups were more likely than patients of non-affiliated groups to receive indicated services for 10 of the 12 HEDIS measures (p
0.05; Table ). Mean performance rate differences between network-affiliated and non-affiliated groups ranged from 2 percentage points (for cervical cancer screening, HbA1c testing, LDL screening, asthma medications, and antidepressant medication management: acute phase) to 14 percentage points (for monitoring diabetic nephropathy). Across the 12 HEDIS measures, there was no consistent relationship between group size and performance scores within either network affiliation category.
Comparison of Mean HEDIS Performance Scores for Patients of Network-affiliated and Non-affiliated Physician Groups
The multivariable models revealed statistically significant relationships between physician group size and performance score for only 3 of the 12 HEDIS measures (data not shown). Compared to other groups, the medium-sized groups had higher performance scores on diabetic eye exams (OR
0.02) and monitoring of diabetic nephropathy (OR
0.02). Compared to large and medium-sized groups, the small groups had lower performance scores on LDL-C screening for patients with diabetes (OR
Network affiliation was consistently associated with higher performance scores in the multivariable models. Patients of network-affiliated groups were more likely to receive HEDIS services than patients of non-affiliated groups on 8 of the 12 HEDIS measures (Table ). Statistically significant odds ratios ranged from 1.10 to 1.97, with differences in mean adjusted performance scores ranging from 2 percentage points (for appropriate asthma medications) to 15 percentage points (for monitoring diabetic nephropathy).
Comparison of Adjusted Mean HEDIS Performance Scores for Patients of Network-affiliated and Non-affiliated Physician Groups
Tests for interactions between group size and network affiliation revealed statistically significant interactions on the 4 HEDIS measures related to diabetes care: HbA1c testing, eye exams, LDL-C screening, and monitoring of diabetic nephropathy. Patients of non-affiliated groups were less likely to receive these 4 services than patients of network-affiliated groups. However, this difference in clinical performance between non-affiliated and network-affiliated groups was of greater magnitude among small groups than among groups in the “medium” and “large” terciles (data not shown). There were no statistically significant interactions between group size and network affiliation for the other 8 HEDIS measures in our analysis.
To ensure that the higher HEDIS performance scores observed for network-affiliated groups were not an artifact of 1 or 2 dominant high-performing or large networks, we calculated adjusted performance scores for each of the 7 networks on all 12 HEDIS measures. Across the 12 measures, 2 networks exhibited higher performance than the others. After excluding data from these 2 networks, statistically significant differences persisted for 6 of the 8 measures for which the main multivariable models showed higher performance scores for network-affiliated groups. After excluding data from the 2 largest networks (which were not the same as the 2 highest performing networks), statistically significant performance score differences persisted for 7 of these 8 measures.