Year	per 1,000
1990	8.7
1991	8.6
1992	8.5
1993	8.5
1994	8.4
1995	8.3
1996	8.2
1997	8.1
1998	8
1999	7.8
2000	7.7
2001	7.6
2002	7.6
2003	7.5
2004	7.5
2005	7.5
2006	7.5
2007	7.5
2008	7.4
2009	7.4
2010	7.3
2011	7.2
2012	7.2
2013	7.1
2014	7
2015	6.8
2016	6.7
2017	6.6
2018	6.5
2019	6.4
2020	6.3
2021	6.2
2022	6.1