Year	per 1,000
1990	7.3
1991	7.2
1992	7.1
1993	6.9
1994	6.8
1995	6.6
1996	6.5
1997	6.4
1998	6.2
1999	6.1
2000	6
2001	5.9
2002	5.8
2003	5.6
2004	5.5
2005	5.4
2006	5.3
2007	5.2
2008	5
2009	4.9
2010	4.8
2011	4.7
2012	4.6
2013	4.5
2014	4.4
2015	4.3
2016	4.2
2017	4.1
2018	4
2019	3.9
2020	3.8
2021	3.7
2022	3.6