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