Year	per 1,000
1990	7.6
1991	7.1
1992	6.8
1993	6.4
1994	6.1
1995	5.8
1996	5.6
1997	5.3
1998	5.1
1999	4.9
2000	4.7
2001	4.5
2002	4.3
2003	4.2
2004	4
2005	3.8
2006	3.7
2007	3.5
2008	3.3
2009	3.2
2010	3
2011	2.9
2012	2.8
2013	2.7
2014	2.6
2015	2.5
2016	2.4
2017	2.3
2018	2.2
2019	2.2
2020	2.1
2021	2
2022	2