Year	per 1,000
1990	8.5
1991	8.4
1992	8.2
1993	8.1
1994	8
1995	8
1996	8
1997	8
1998	8
1999	8
2000	8
2001	8
2002	8
2003	8
2004	8
2005	7.9
2006	7.9
2007	7.9
2008	7.8
2009	7.8
2010	7.7
2011	7.7
2012	7.6
2013	7.6
2014	7.5
2015	7.4
2016	7.3
2017	7.2
2018	7.1
2019	7
2020	6.9
2021	6.7
2022	6.6