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