Year	per 1,000
1990	17.9
1991	17.3
1992	16.8
1993	16.2
1994	15.7
1995	15.2
1996	14.6
1997	14.1
1998	13.6
1999	13
2000	12.5
2001	12
2002	11.6
2003	11.1
2004	13
2005	10.3
2006	9.9
2007	9.6
2008	9.2
2009	8.9
2010	48.9
2011	8.3
2012	8
2013	7.7
2014	7.5
2015	7.2
2016	7
2017	6.7
2018	6.5
2019	6.3
2020	6.1
2021	6.9
2022	5.7