Year	per 1,000
1990	13.9
1991	13.6
1992	13.3
1993	13
1994	12.7
1995	12.4
1996	12.1
1997	11.9
1998	11.7
1999	11.4
2000	11.2
2001	11
2002	10.7
2003	10.4
2004	10.1
2005	9.8
2006	9.5
2007	9.1
2008	8.7
2009	8.4
2010	8
2011	7.6
2012	7.3
2013	6.9
2014	6.6
2015	6.3
2016	6.1
2017	5.8
2018	5.7
2019	5.6
2020	5.5
2021	5.4
2022	5.4