Year	per 1,000
1990	18.7
1991	18.8
1992	18.9
1993	19
1994	19.1
1995	19.2
1996	19.1
1997	19.1
1998	18.8
1999	18.5
2000	18.1
2001	17.5
2002	16.9
2003	16.3
2004	15.6
2005	15.1
2006	14.5
2007	13.9
2008	13.4
2009	13
2010	12.5
2011	12.1
2012	11.7
2013	11.3
2014	11
2015	10.7
2016	10.3
2017	10.1
2018	9.8
2019	9.5
2020	9.3
2021	9
2022	8.7