Year	per 1,000
1990	5.4
1991	5.6
1992	5.8
1993	6
1994	6.2
1995	6.4
1996	6.4
1997	6.3
1998	6.2
1999	6
2000	5.8
2001	5.6
2002	5.4
2003	5.4
2004	5.4
2005	5.5
2006	5.5
2007	5.3
2008	5.1
2009	4.7
2010	4.4
2011	4.1
2012	3.9
2013	3.7
2014	3.5
2015	3.3
2016	3.1
2017	3
2018	3
2019	3
2020	2.9
2021	2.9
2022	2.8