Year	per 1,000 people
1960	0.396
1965	0.335
1970	0.348
1975	0.351
1977	0.637
1990	0.936
1991	1.142
1992	1.178
1993	1.091
1994	1.258
1995	1.234
1996	1.307
1997	1.324
1998	1.313
1999	1.376
2000	1.452
2001	1.552
2002	1.575
2003	1.505
2009	1.602
2010	2.114
2011	1.659
2015	2.067
2016	2.043
2017	2.232