Year	per 1,000
1990	10
1991	9.8
1992	9.7
1993	9.5
1994	9.3
1995	9.2
1996	9.1
1997	8.9
1998	8.8
1999	8.7
2000	8.6
2001	8.5
2002	8.4
2003	8.3
2004	8.2
2005	8.1
2006	8
2007	7.9
2008	7.8
2009	7.6
2010	7.5
2011	7.4
2012	7.3
2013	7.2
2014	7.1
2015	6.9
2016	6.8
2017	6.7
2018	6.6
2019	6.5
2020	6.4
2021	6.3
2022	6.2