Year	per 1,000
1990	13.9
1991	13.4
1992	13
1993	12.5
1994	12.1
1995	11.7
1996	11.3
1997	10.9
1998	10.6
1999	10.3
2000	9.9
2001	9.6
2002	9.4
2003	9.1
2004	8.8
2005	8.6
2006	8.4
2007	8.2
2008	8
2009	7.8
2010	7.6
2011	7.5
2012	7.3
2013	7.1
2014	7
2015	6.8
2016	6.7
2017	6.5
2018	6.4
2019	6.2
2020	6.1
2021	5.9
2022	5.8