Year	per 1,000
1990	5.5
1991	5.2
1992	5
1993	4.7
1994	4.5
1995	4.4
1996	4.3
1997	4.2
1998	4.2
1999	4.1
2000	4.1
2001	4
2002	4
2003	4
2004	4
2005	4
2006	4.1
2007	4.1
2008	4.2
2009	4.2
2010	4.1
2011	4
2012	3.9
2013	3.8
2014	3.8
2015	3.8
2016	3.7
2017	3.7
2018	3.7
2019	3.7
2020	3.7
2021	3.9
2022	4