Table 7 Aggregation errors in measures of the accessibility of hospitals at the census tract level
Absolute difference between accessibility measure obtained from CTCa and WBL2b aggregation methods | Mean | Percentiles (%) | ||||||
|---|---|---|---|---|---|---|---|---|
5 | 10 | 25 | 50 | 75 | 90 | 95 | ||
Euclidean distance (m) | ||||||||
 Minimum time distance | 236.35 | 5.24 | 11.17 | 33.29 | 88.44 | 218.39 | 649.26 | 1104.88 |
 Average distance to all services | 202.62 | 2.05 | 4.01 | 13.41 | 42.99 | 146.13 | 617.01 | 1022.88 |
 Average distance to three closest services | 189.97 | 3.01 | 6.15 | 16.40 | 47.73 | 159.28 | 527.03 | 963.20 |
 Average distance to five closest services | 184.45 | 3.05 | 5.42 | 15.31 | 46.69 | 140.41 | 530.94 | 997.41 |
 Number of services within 500 m | 0.05 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.17 | 0.43 |
 Number of services within 1000 m | 0.10 | 0.00 | 0.00 | 0.00 | 0.00 | 0.04 | 0.37 | 0.59 |
 Number of services within 2000 m | 0.17 | 0.00 | 0.00 | 0.00 | 0.00 | 0.25 | 0.56 | 0.82 |
 Potential gravity model (friction parameter = 1) | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
 Potential gravity model (friction parameter = 1.5) | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
 Potential gravity model (friction parameter = 2) | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
 2SFCA (2000 m or 30 min) | 0.22 | 0.00 | 0.00 | 0.01 | 0.06 | 0.23 | 0.57 | 1.09 |
 E2SFCA with a slow step-decay function | 1.93 | 0.00 | 0.00 | 0.00 | 0.02 | 1.47 | 5.73 | 9.53 |
 E2SFCA with a fast step-decay functiona | 4.07 | 0.00 | 0.00 | 0.00 | 0.19 | 2.54 | 10.05 | 16.20 |
 E2SFCA with a gradient function | 1.97 | 0.00 | 0.00 | 0.00 | 0.08 | 1.41 | 5.91 | 9.73 |
Shortest network time (on foot) (min) | ||||||||
 Minimum time distance | 4.17 | 0.10 | 0.25 | 0.67 | 1.61 | 3.65 | 10.22 | 17.17 |
 Average distance to all services | 3.49 | 0.05 | 0.12 | 0.34 | 1.00 | 2.72 | 9.37 | 16.48 |
 Average distance to three closest services | 3.55 | 0.07 | 0.15 | 0.40 | 1.18 | 3.05 | 8.97 | 15.62 |
 Average distance to five closest services | 3.44 | 0.07 | 0.14 | 0.36 | 1.05 | 2.86 | 8.30 | 15.48 |
 Number of services within 10 min | 0.06 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.24 | 0.45 |
 Number of services within 20 min | 0.12 | 0.00 | 0.00 | 0.00 | 0.00 | 0.11 | 0.46 | 0.68 |
 Number of services within 30 min | 0.17 | 0.00 | 0.00 | 0.00 | 0.00 | 0.22 | 0.58 | 0.83 |
 Potential gravity model (friction parameter = 1) | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
 Potential gravity model (friction parameter = 1.5) | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
 Potential gravity model (friction parameter = 2) | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
 2SFCA (2000 m or 30 min) | 0.92 | 0.00 | 0.00 | 0.00 | 0.00 | 0.56 | 2.59 | 4.83 |
 E2SFCA with a slow step-decay function | 1.70 | 0.00 | 0.00 | 0.00 | 0.01 | 1.06 | 3.95 | 7.67 |
 E2SFCA with a fast step-decay functiona | 3.29 | 0.00 | 0.00 | 0.00 | 0.04 | 1.85 | 7.33 | 13.20 |
 E2SFCA with a gradient function | 2.27 | 0.00 | 0.00 | 0.00 | 0.01 | 1.22 | 4.71 | 10.38 |