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Table 7 Aggregation errors in measures of the accessibility of hospitals at the census tract level

From: The approaches to measuring the potential spatial access to urban health services revisited: distance types and aggregation-error issues

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
  1. aAggregation method based on census tract centroid (the least accurate method)
  2. bAggregation method based on the population-weighted mean of the accessibility measure for block centroids (adjusted with the land use map) within census tracts (the most accurate method)