Table 4.
Adjusted mean MA plan premiums by degree of MA market concentration, degree of hospital market concentration, and plan qualitya
| Mean MA market concentrationb | I | II | III | IV | V | VI | VII | VIII | IX |
|---|---|---|---|---|---|---|---|---|---|
| Lower‐quality plans (summary score < 4 stars) | High‐quality plans (summary score ≥ 4 stars) | ||||||||
| All plans | Lower‐quality plans (summary score <4 stars) | High‐quality plans (summary score ≥4 stars) | Concentrated Hospital Market (HHI ≥ 2500)c | Competitive Hospital Market (HHI < 2500)c | Concentrated Hospital Market (HHI ≥ 2500) | Competitive Hospital Market (HHI < 2500) | Concentrated Hospital Market (HHI ≥ 2500) | Competitive Hospital Market (HHI < 2500) | |
| MA HHIb = 100 | $31.25 (22.49‐40.02) | $32.09 (22.42‐41.76) | $29.98 (14.89‐45.07) | $39.22 (29.30‐49.15) | $13.56 (3.70‐23.42) | $40.64 (30.30‐50.97) | $13.75 (2.24‐25.25) | $37.11 (20.96‐53.26) | $13.25 (0.17‐28.07) |
| MA HHI = 2500 | $42.38 (39.10‐45.66) | $37.01 (33.41‐40.60) | $50.63 (44.87‐56.39) | $48.17 (44.18‐52.17) | $29.50 (25.80‐33.20) | $43.24 (38.95‐47.53) | $23.62 (19.62‐27.63) | $55.55 (49.37‐61.74) | $39.09 (33.07‐45.11) |
| MA HHI = 5000 | $53.96 (48.47‐59.45) | $42.13 (35.92‐48.33) | $72.15 (62.23‐82.06) | $57.50 (51.97‐63.02) | $46.10 (38.00‐54.20) | $45.95 (40.16‐51.74) | $33.91 (24.75‐43.08) | $74.76 (64.47‐85.06) | $66.01 (55.15‐76.87) |
| MA HHI = 7500 | $65.54 (53.72‐77.36) | $47.25 (33.98‐60.51) | $93.66 (72.76‐114.56) | $66.82 (54.67‐78.98) | $62.70 (46.59‐78.81) | $48.67 (36.09‐61.24) | $44.20 (25.63‐62.77) | $93.98 (72.07‐115.88) | $92.92 (71.07‐114.78) |
| MA HHI = 10 000 | $77.12 (58.71‐95.54) | $52.37 (31.75‐72.98) | $115.18 (82.79‐147.55) | $76.15 (56.97‐95.32) | $79.30 (54.91‐103.70) | $51.38 (31.57‐71.18) | $54.49 (26.23‐82.75) | $113.19 (79.14‐147.23) | $119.84 (86.43‐153.24) |
Full regression model results can be viewed in Table S3.
Adjusted mean premiums calculated in Stata v.14, applying the margins command to ordinary least‐squares linear regression models based on Equation (b). Regression models include interactions between MA market concentration and hospital market concentration and MA market concentration and quality rating.
MA HHI is Medicare Advantage health insurance market concentration, as measured by the Herfindahl‐Hirschman Index (HHI), with counties serving as the relevant geographic market and each insurance company's county‐level MA enrollment serving as the measure of market share. The unit of analysis is the MA plan level, so for the analyses that underpin the predicted probabilities presented in this table, HHI was enrollment‐weighted and aggregated to the plan level to calculate mean HHI across each plan's service area.
Hospital market concentration was measured by calculating HHIs with geographic markets set at the core‐based statistical area (CBSA) level and with market shares defined using each hospital's total annual Medicare days. As above, hospital HHI was enrollment‐weighted and aggregated to the plan level to calculate mean hospital HHI across each plan's service area. The analyses then differentiated between plans that tend to operate in more concentrated hospital markets (hospital HHI ≥ 2500) and those that tend to operate in more competitive hospital markets (hospital HHI < 2500).