Year	per 1,000
1990	6.3
1991	6.3
1992	6.4
1993	6.5
1994	6.6
1995	6.7
1996	6.8
1997	7
1998	7.1
1999	7.2
2000	7.4
2001	7.5
2002	7.6
2003	7.7
2004	7.8
2005	7.9
2006	8
2007	8
2008	8.1
2009	8.1
2010	8.1
2011	8.1
2012	8
2013	7.9
2014	7.9
2015	7.8
2016	7.7
2017	7.7
2018	7.6
2019	7.6
2020	7.5
2021	7.4
2022	7.2