Year	per 1,000
1990	4.7
1991	5.2
1992	4.3
1993	4.1
1994	3.9
1995	3.7
1996	3.6
1997	3.4
1998	3.3
1999	3.2
2000	3
2001	2.9
2002	2.8
2003	2.7
2004	2.7
2005	2.6
2006	2.6
2007	2.5
2008	2.5
2009	2.4
2010	2.4
2011	2.4
2012	2.3
2013	2.9
2014	2.3
2015	2.2
2016	2.2
2017	2.2
2018	2.1
2019	2.1
2020	2.1
2021	2
2022	2