Year	per 1,000
1990	10.6
1991	10.4
1992	10.3
1993	10.2
1994	10.1
1995	9.9
1996	9.8
1997	9.7
1998	9.6
1999	9.5
2000	9.3
2001	9.2
2002	9.1
2003	9
2004	8.9
2005	8.8
2006	8.8
2007	8.7
2008	8.6
2009	8.6
2010	8.5
2011	8.4
2012	8.3
2013	8.2
2014	8.1
2015	8
2016	7.9
2017	7.7
2018	7.6
2019	7.5
2020	7.3
2021	7.2
2022	7.1