Year	per 1,000
1990	4.6
1991	4.7
1992	4.8
1993	4.9
1994	4.9
1995	4.8
1996	4.7
1997	4.6
1998	4.4
1999	4.3
2000	4.2
2001	4.1
2002	4
2003	4
2004	4
2005	4.2
2006	4.4
2007	4.7
2008	5.1
2009	5.3
2010	5.4
2011	5.4
2012	5.3
2013	5.1
2014	4.8
2015	4.5
2016	4.2
2017	4
2018	3.9
2019	3.8
2020	3.7
2021	3.6
2022	3.5