Year	per 1,000
1990	2.8
1991	2.7
1992	2.6
1993	2.6
1994	2.5
1995	2.4
1996	2.4
1997	2.4
1998	2.4
1999	2.3
2000	2.3
2001	2.2
2002	2
2003	1.9
2004	1.8
2005	1.7
2006	1.6
2007	1.5
2008	1.5
2009	1.4
2010	1.4
2011	1.3
2012	1.2
2013	1.2
2014	1.1
2015	1.1
2016	1.1
2017	1.1
2018	1
2019	1
2020	1
2021	1
2022	1