Year	per 1,000
1990	10.5
1991	10.3
1992	10.2
1993	10
1994	9.9
1995	9.8
1996	9.7
1997	9.6
1998	9.4
1999	9.3
2000	9.1
2001	9
2002	8.8
2003	8.6
2004	8.5
2005	8.3
2006	8.1
2007	7.9
2008	7.7
2009	7.5
2010	7.2
2011	7
2012	6.8
2013	6.6
2014	6.4
2015	6.2
2016	6
2017	5.8
2018	5.6
2019	5.5
2020	5.3
2021	5.1
2022	5