Year	per 1,000 people
1960	1.8449837295145264
1970	1.9132313316957892
1980	1.7561565950241553
1981	1.7541120950407536
1990	1.7522383307353393
2005	1.7693946173590436
2006	1.5847432589061126
2009	1.5842793837592861