Year	per 1,000
1990	9
1991	8.8
1992	8.6
1993	8.5
1994	8.4
1995	8.3
1996	8.2
1997	8.1
1998	8.1
1999	8
2000	8
2001	8
2002	8
2003	7.9
2004	7.7
2005	7.6
2006	7.5
2007	7.5
2008	7.5
2009	7.6
2010	8.2
2011	7.5
2012	7.4
2013	7.3
2014	7.2
2015	7.2
2016	7.2
2017	7.2
2018	7.2
2019	7.1
2020	7.1
2021	7.1
2022	7.1