Year	per 1,000
1990	13.3
1991	13.1
1992	13
1993	12.9
1994	12.8
1995	12.7
1996	12.5
1997	12.5
1998	12.4
1999	12.3
2000	12.2
2001	12.1
2002	12
2003	11.9
2004	11.9
2005	11.8
2006	11.7
2007	11.6
2008	11.5
2009	11.5
2010	11.4
2011	11.3
2012	11.3
2013	11.2
2014	11.1
2015	11
2016	10.9
2017	10.8
2018	10.7
2019	10.6
2020	10.4
2021	10.3
2022	10