Year	per 1,000
1990	10.5
1991	7.5
1992	7
1993	6.6
1994	6.3
1995	6
1996	5.7
1997	5.5
1998	5.3
1999	5.2
2000	5.2
2001	5.1
2002	5.2
2003	6.6
2004	5.2
2005	5.3
2006	5.3
2007	5.5
2008	5.6
2009	5.5
2010	5.4
2011	5.1
2012	4.8
2013	4.6
2014	4.4
2015	4.4
2016	4.5
2017	4.6
2018	4.7
2019	4.8
2020	4.7
2021	4.7
2022	4.6