Year	per 1,000
1990	6.1
1991	6.2
1992	6.3
1993	6.3
1994	6.3
1995	6.4
1996	6.4
1997	8.5
1998	6.5
1999	6.5
2000	6.5
2001	6.6
2002	6.6
2003	6.7
2004	6.8
2005	6.8
2006	6.9
2007	7
2008	7
2009	7.1
2010	7.1
2011	7.1
2012	7
2013	6.9
2014	6.8
2015	6.7
2016	6.6
2017	6.5
2018	6.4
2019	6.3
2020	6.1
2021	6
2022	5.9