Year	per 1,000
1990	5.4
1991	5.3
1992	5.3
1993	5.2
1994	5.2
1995	5.1
1996	4.9
1997	4.7
1998	4.6
1999	4.5
2000	4.5
2001	4.5
2002	4.6
2003	4.6
2004	4.7
2005	4.7
2006	4.7
2007	4.6
2008	4.5
2009	4.3
2010	4.2
2011	4.1
2012	4
2013	4.1
2014	4.2
2015	4.3
2016	4.4
2017	4.4
2018	4.5
2019	4.7
2020	5
2021	5.4
2022	5.9