Year	per 1,000
1990	2.7
1991	2.7
1992	2.7
1993	2.6
1994	2.6
1995	2.6
1996	2.5
1997	2.5
1998	2.5
1999	2.5
2000	2.4
2001	2.4
2002	2.3
2003	2.3
2004	2.3
2005	2.2
2006	2.2
2007	2.1
2008	2
2009	1.9
2010	1.8
2011	1.7
2012	1.6
2013	1.5
2014	1.4
2015	1.3
2016	1.2
2017	1.2
2018	1.1
2019	1.1
2020	1.1
2021	1
2022	1