Year	per 1,000
1990	1.9
1991	1.8
1992	1.8
1993	1.7
1994	1.7
1995	1.6
1996	1.6
1997	1.5
1998	1.5
1999	1.4
2000	1.4
2001	1.4
2002	1.3
2003	1.3
2004	1.3
2005	1.3
2006	1.2
2007	1.2
2008	1.2
2009	1.2
2010	1.1
2011	1.1
2012	1.1
2013	1.1
2014	1.1
2015	1.1
2016	1
2017	1
2018	1
2019	1
2020	0.9
2021	0.9
2022	0.9