Year	per 1,000
1990	7.8
1991	7.6
1992	7.4
1993	7.2
1994	7.1
1995	6.9
1996	6.8
1997	6.6
1998	11.7
1999	6.3
2000	6.2
2001	6
2002	5.9
2003	5.8
2004	5.6
2005	5.5
2006	5.4
2007	5.3
2008	5.2
2009	5.1
2010	5
2011	4.9
2012	4.8
2013	4.7
2014	4.6
2015	4.5
2016	4.4
2017	4.4
2018	4.3
2019	4.2
2020	4.1
2021	4.1
2022	4