Year	per 1,000
1990	17.4
1991	17.1
1992	16.8
1993	16.5
1994	16.1
1995	15.7
1996	15.3
1997	14.9
1998	14.5
1999	14
2000	13.5
2001	13
2002	12.5
2003	12
2004	11.5
2005	11
2006	10.6
2007	10.2
2008	9.8
2009	9.4
2010	9.1
2011	8.7
2012	8.5
2013	8.4
2014	8.4
2015	8.4
2016	8.4
2017	8.4
2018	8.4
2019	8.4
2020	8.4
2021	8.4
2022	8.4