Year	per 1,000
1990	4.5
1991	4.5
1992	4.4
1993	4.3
1994	4.2
1995	4.1
1996	4
1997	3.9
1998	3.8
1999	3.8
2000	3.7
2001	3.6
2002	3.6
2003	3.5
2004	3.5
2005	3.5
2006	3.4
2007	3.4
2008	3.3
2009	3.2
2010	3.1
2011	3.1
2012	3
2013	2.9
2014	2.9
2015	2.9
2016	2.9
2017	2.9
2018	3
2019	3
2020	3.1
2021	3.3
2022	3.5