Year	per 1,000
1990	10.1
1991	9.9
1992	9.6
1993	9.4
1994	9.2
1995	8.9
1996	8.7
1997	8.5
1998	8.4
1999	8.2
2000	8.1
2001	7.9
2002	7.8
2003	7.7
2004	7.7
2005	7.7
2006	7.6
2007	7.6
2008	7.6
2009	7.6
2010	7.6
2011	7.5
2012	7.4
2013	7.3
2014	7.2
2015	7.1
2016	7
2017	6.9
2018	6.8
2019	6.7
2020	6.6
2021	6.5
2022	6.4