Table 1.
Summary statistics of the compiled data.
| Frequency | Percent | |
|---|---|---|
| Explanatory variables | ||
| Study was conducted in Europe, North America or Oceania | ||
| No (0) | 82 | 28.0 |
| Yes (1) | 211 | 72.0 |
| Study published after 2005 | ||
| No (0) | 73 | 24.9 |
| Yes (1) | 220 | 75.1 |
| City population is less than 500,000 inhabitants | ||
| No (0) | 186 | 63.5 |
| Yes (1) | 107 | 36.5 |
| Traffic contribution estimates were based on PM10 | ||
| No (0) | 182 | 62.1 |
| Yes (1) | 111 | 37.9 |
| Number of records in each region | ||
| Africa | 4 | 1.4 |
| Central and Eastern Europe | 5 | 1.7 |
| East Asia | 34 | 11.6 |
| India | 6 | 2.0 |
| Middle East | 7 | 2.4 |
| North America | 62 | 21.2 |
| Northwestern Europe | 24 | 8.2 |
| Oceania | 8 | 2.7 |
| South and Central America | 17 | 5.8 |
| Southeastern Asia | 9 | 3.1 |
| Southern Asia | 5 | 1.7 |
| Southwestern Europe | 95 | 32.4 |
| Western Europe | 17 | 5.8 |
| Note: Total number of observations is 293. | ||