Year	per 1,000
1990	2.8
1991	2.8
1992	2.7
1993	2.7
1994	2.7
1995	2.7
1996	2.7
1997	2.7
1998	2.7
1999	2.7
2000	2.7
2001	2.6
2002	2.6
2003	2.6
2004	2.6
2005	2.5
2006	2.5
2007	2.5
2008	2.4
2009	2.4
2010	2.4
2011	2.3
2012	2.3
2013	2.2
2014	2.2
2015	2.1
2016	2.1
2017	2
2018	1.9
2019	1.9
2020	1.8
2021	1.8
2022	1.8