Year	per 1,000
1990	8.3
1991	8.5
1992	8.7
1993	8.7
1994	8.5
1995	8.2
1996	7.9
1997	7.7
1998	7.5
1999	7.5
2000	7.5
2001	7.5
2002	7.6
2003	7.7
2004	7.8
2005	7.9
2006	8
2007	8
2008	8
2009	7.9
2010	7.7
2011	7.4
2012	7.1
2013	6.8
2014	6.5
2015	6.4
2016	6.4
2017	6.4
2018	6.4
2019	6.5
2020	6.6
2021	6.6
2022	6.6