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