Year	per 1,000
1990	17.9
1991	17.2
1992	16.6
1993	16
1994	15.4
1995	14.7
1996	14.2
1997	13.6
1998	13
1999	12.5
2000	12
2001	11.4
2002	10.9
2003	10.5
2004	10.1
2005	9.8
2006	9.5
2007	9.2
2008	9
2009	8.7
2010	40.4
2011	8.3
2012	8.1
2013	7.9
2014	7.7
2015	7.4
2016	7.2
2017	7
2018	6.9
2019	6.7
2020	6.5
2021	6.4
2022	6.3