Year	per 1,000
1990	18.4
1991	17.6
1992	16.9
1993	16.2
1994	15.6
1995	15
1996	14.3
1997	13.7
1998	13.2
1999	12.6
2000	12
2001	11.5
2002	11.1
2003	10.6
2004	10.2
2005	9.8
2006	9.4
2007	9.1
2008	8.8
2009	8.5
2010	8.2
2011	7.9
2012	7.7
2013	7.4
2014	7.2
2015	7
2016	6.8
2017	6.6
2018	6.4
2019	6.3
2020	6.2
2021	6
2022	5.8