Year	per 1,000
1990	5.1
1991	5.3
1992	3
1993	3.1
1994	3.2
1995	3.2
1996	3.2
1997	3.1
1998	3.1
1999	3
2000	2.9
2001	2.8
2002	2.7
2003	2.7
2004	2.6
2005	2.6
2006	2.6
2007	2.5
2008	2.5
2009	2.5
2010	2.5
2011	2.4
2012	2.4
2013	2.4
2014	2.4
2015	2.3
2016	2.3
2017	2.2
2018	2.2
2019	2.1
2020	2
2021	2
2022	1.9