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