Year	per 1,000
1990	5
1991	5
1992	5
1993	4.9
1994	4.9
1995	4.8
1996	4.7
1997	4.5
1998	4.4
1999	4.3
2000	4.2
2001	4.2
2002	4.1
2003	4.1
2004	4.1
2005	4.1
2006	4.1
2007	4.2
2008	4.2
2009	4.3
2010	4.3
2011	4.3
2012	4.4
2013	4.4
2014	4.5
2015	4.5
2016	4.6
2017	4.6
2018	4.7
2019	4.7
2020	4.8
2021	4.8
2022	4.8