Year	per 1,000
1990	8.3
1991	8.2
1992	8
1993	7.9
1994	7.8
1995	7.6
1996	7.5
1997	7.4
1998	7.2
1999	7.1
2000	6.9
2001	6.8
2002	6.6
2003	6.5
2004	6.3
2005	6.2
2006	6.1
2007	5.9
2008	5.8
2009	5.7
2010	5.6
2011	5.4
2012	5.3
2013	5.2
2014	5.1
2015	5
2016	4.9
2017	4.9
2018	4.8
2019	4.7
2020	4.6
2021	4.5
2022	4.3