Year	per 1,000
1990	2.1
1991	2.1
1992	2
1993	2
1994	1.9
1995	1.9
1996	1.8
1997	1.8
1998	1.8
1999	1.7
2000	1.7
2001	1.7
2002	1.6
2003	1.6
2004	1.6
2005	1.5
2006	1.5
2007	1.4
2008	1.4
2009	1.4
2010	1.3
2011	1.3
2012	1.3
2013	1.2
2014	1.2
2015	1.2
2016	1.1
2017	1.1
2018	1.1
2019	1
2020	1
2021	1
2022	1