Year	per 1,000
1990	4.6
1991	4.5
1992	4.4
1993	4.4
1994	4.3
1995	4.2
1996	4.2
1997	4.1
1998	4
1999	3.9
2000	3.7
2001	3.6
2002	3.6
2003	3.5
2004	3.5
2005	3.5
2006	3.6
2007	3.7
2008	4
2009	4.2
2010	4.4
2011	4.4
2012	4.2
2013	3.9
2014	3.8
2015	3.7
2016	3.8
2017	3.9
2018	4.1
2019	4.2
2020	4.2
2021	4.2
2022	4.1