Year	per 1,000
1990	5.1
1991	5.1
1992	5.1
1993	5.1
1994	5.1
1995	5.2
1996	5.2
1997	5.3
1998	5.3
1999	5.4
2000	5.5
2001	5.6
2002	5.7
2003	5.7
2004	5.8
2005	5.9
2006	6
2007	6
2008	6.1
2009	6.2
2010	6.3
2011	6.4
2012	6.5
2013	6.6
2014	6.7
2015	6.8
2016	6.8
2017	6.9
2018	6.8
2019	6.7
2020	6.7
2021	6.5
2022	6.4