Year	per 1,000
1990	5.6
1991	5.7
1992	6.4
1993	6.6
1994	6.4
1995	6.6
1996	6.2
1997	6.1
1998	6.2
1999	6.3
2000	6.2
2001	6
2002	5.8
2003	5.6
2004	5.4
2005	5.2
2006	5
2007	4.9
2008	4.6
2009	4.4
2010	4.1
2011	3.9
2012	3.7
2013	3.5
2014	3.4
2015	3.2
2016	3
2017	2.8
2018	2.7
2019	2.7
2020	2.7
2021	2.7
2022	3.5