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