Year	per 1,000 people
1960	2.75537443161011
1970	3.81369996070862
1981	4.82550001144409
1990	4.1729998589
1997	4.3000001907
2000	4.12
2001	3.85
2002	3.9
2003	3.9
2004	3.9
2005	3.4
2006	3.7
2007	3.7
2008	3.7
2009	3.7
2010	3.7
2011	3.7
2012	3.7
2013	3.7
2014	3.7
2015	3.7
2016	3.7
2017	3.2