Year	per 1,000
1990	7.7
1991	7.8
1992	7.8
1993	7.8
1994	7.9
1995	7.9
1996	7.9
1997	8
1998	8
1999	8.1
2000	8.1
2001	8.2
2002	8.2
2003	8.3
2004	8.4
2005	8.5
2006	8.5
2007	8.5
2008	8.5
2009	8.4
2010	8.3
2011	8.2
2012	8
2013	7.8
2014	7.7
2015	7.5
2016	7.3
2017	7.1
2018	7
2019	6.8
2020	6.7
2021	6.5
2022	6.4