Year	per 1,000
1990	3.3
1991	3.4
1992	3.6
1993	3.7
1994	3.7
1995	3.8
1996	3.8
1997	4.6
1998	3.8
1999	3.6
2000	3.4
2001	3.1
2002	2.9
2003	2.7
2004	2.6
2005	2.6
2006	2.6
2007	2.6
2008	2.6
2009	2.6
2010	2.6
2011	2.6
2012	2.5
2013	2.4
2014	2.3
2015	2.1
2016	2
2017	1.9
2018	1.8
2019	1.7
2020	1.6
2021	1.6
2022	1.5