Year	per 1,000
1990	7.7
1991	7.6
1992	7.5
1993	7.4
1994	7.3
1995	7.2
1996	7.1
1997	7
1998	7
1999	6.9
2000	6.9
2001	6.8
2002	6.8
2003	6.8
2004	6.7
2005	6.7
2006	6.7
2007	6.6
2008	6.5
2009	6.5
2010	6.4
2011	6.3
2012	6.2
2013	6.1
2014	6
2015	5.9
2016	5.8
2017	5.7
2018	5.6
2019	5.6
2020	5.5
2021	5.4
2022	5.3