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