Table 2.
Comparison of Trip Duration (in Minutes) from Log and GPS
| N (trips) |
Mean±SD | Median | Min, Max | N (%) trips GPS<Log |
N (%) trips <10 min difference |
Concordance index [95% CI] (Natural log scale)a |
Bland&Altman [95% Limits of agreement]b |
|
|---|---|---|---|---|---|---|---|---|
| Total | ||||||||
| GPS | 1139 | 13.9 ± 11.0 | 10.9 | 0.1, 90 | ||||
| Log | 1139 | 18.3 ± 20.2 | 15.0 | 0, 359 | ||||
| Abs. Diff. | 1139 | 7.5 ± 17.5 | 4.1 | 0, 358.4 | 773 (67%) | 931 (81%) | 0.53 [0.47, 0.59] |
0.76 [0.16, 3.71] |
| Weekday | ||||||||
| GPS | 742 | 13.8 ± 10.9 | 11.1 | 0.1, 76.9 | ||||
| Log | 742 | 18.5 ± 22.0 | 15.0 | 0, 359 | ||||
| Abs. Diff. | 742 | 8.0 ± 20.1 | 4.0 | 0, 358.4 | 505 (68%) | 590 (80%) | 0.50 [0.43, 0.55] |
0.74 [0.14, 4.08] |
| Weekend | ||||||||
| GPS | 409 | 14.1 ± 11.2 | 10.7 | 0.6, 90 | ||||
| Log | 409 | 17.9 ± 16.6 | 15.0 | 0, 165 | ||||
| Abs. Diff. | 409 | 6.6 ± 11.4 | 4.2 | 0.1,139.9 | 268 (66%) | 341 (83%) | 0.63 [0.56, 0.69] |
0.79 [0.21, 3.04] |
a
Log of Zeros not defined, therefore zero minutes were included as zeros.
b
Limits of agreement for the ratio after log values were back transformed.
Abs. Diff.=Absolute difference.