Year	per 1,000
1990	27.5
1991	4.8
1992	4.7
1993	4.6
1994	4.5
1995	4.4
1996	4.4
1997	4.3
1998	4.2
1999	4.1
2000	4.1
2001	4
2002	3.9
2003	3.8
2004	3.8
2005	3.7
2006	6.4
2007	3.6
2008	3.5
2009	3.5
2010	3.5
2011	3.4
2012	3.4
2013	3.4
2014	3.4
2015	3.5
2016	3.5
2017	4
2018	3.6
2019	3.7
2020	3.7
2021	3.8
2022	3.9