Year	per 1,000
1990	4.9
1991	4.5
1992	4.1
1993	3.8
1994	3.6
1995	3.4
1996	3.2
1997	3.1
1998	3
1999	2.8
2000	2.7
2001	2.6
2002	2.5
2003	2.4
2004	2.3
2005	2.3
2006	2.4
2007	2.4
2008	2.5
2009	2.5
2010	2.5
2011	2.5
2012	2.5
2013	2.4
2014	2.4
2015	2.3
2016	2.2
2017	2.2
2018	2.1
2019	2
2020	2
2021	1.9
2022	1.8