| Country | Reference of Study | Year |
| France | | 1992 |
| USA | | 1993 |
| Germany | | 1987 |
| Britain | | 1987 |
| Sweden | | 1990 |
| Singapore | | 1992 |
| South Korea | | 1990 |
| Australia | | 1983 |
| Ireland | | 1992 |