Table 2.
Final model of effective factors in the frequency of motorcycle accidents leading to death in Tehran, 2011–2016.
| Variable | coefficienta | p value | Confidence interval coefficient of 95% |
|
|---|---|---|---|---|
| Maximum | Minimum | |||
| Population Density (km2) | −155.962 | <0.001 | −76.927 | −234.997 |
| Population of illiterate people | 6.97e-05 | <0.001 | 10.04e-05 | 3.89e-05 |
| Number of parks | −0.016 | 0.002 | −0.006 | −0.026 |
| The ratio of the length of the highways to the total length of the passages | 2.211 | 0.002 | 3.605 | 0.816 |
| Land use | −2.95e-08 | 0.033 | −2.33e-09 | −5.67e-08 |
| Industrial use | 8.72e-07 | 0.003 | 1.44e-06 | 3.01e-07 |
| Commercial use | −1.52e-06 | 0.019 | −2.49e-07 | −2.78e-06 |
| Transportation and Warehouse use | −1.06e-06 | <0.001 | −5.85e-07 | −1.53e-06 |
| Educational use | 1.39e-06 | 0.061 | 2.85e-06 | −6.40e-08 |
| The ratio of the length of arterial streets to the total length of the passages | 0.245 | 0.162 | 0.590 | −0.098 |
| Traffic volume | 0.041 | 0.001 | 0.066 | 0.015 |
| Number of students at the residential place | 0.001 | 0.028 | 0.002 | 0.0001 |
| Ramp and loop ratio to the total length of the passages | −0.039 | 0.125 | 0.010 | −0.090 |
| Model evaluation criteria | ||||
| AIC | 6.18 | |||
| BIC | 84.32 | |||
AIC: Akaike's information criterion, BIC: Bayesian information criterion.
a
In the Poisson model and the negative binomial with a unit of change in the independent variable of the corresponding logarithm of the response variable varies based on the size of the corresponding variable coefficient, provided that other variables remain constant in the model. For example, if personal ownership per capita increases one unit in the spatial units under study, the number of incidents leading to injuries will drop by as much as 0.8, because its coefficient is less than one.