Year	per 1,000
1990	19.3
1991	18.7
1992	18.2
1993	17.8
1994	17.4
1995	17.2
1996	16.9
1997	16.7
1998	16.6
1999	16.4
2000	16.3
2001	16.1
2002	15.9
2003	15.7
2004	15.4
2005	15.1
2006	14.8
2007	14.5
2008	14.1
2009	13.8
2010	13.5
2011	13.2
2012	12.9
2013	12.6
2014	12.3
2015	12
2016	11.7
2017	11.4
2018	11
2019	10.7
2020	10.5
2021	10.1
2022	9.8