Year	per 1,000
1990	2.7
1991	2.7
1992	2.7
1993	2.7
1994	2.7
1995	2.7
1996	2.6
1997	2.6
1998	2.5
1999	2.5
2000	2.4
2001	2.4
2002	2.3
2003	2.3
2004	2.3
2005	2.3
2006	2.3
2007	2.2
2008	2.2
2009	2.1
2010	2
2011	1.9
2012	1.8
2013	1.7
2014	1.6
2015	1.6
2016	1.5
2017	1.5
2018	1.4
2019	1.4
2020	1.4
2021	1.4
2022	1.3