Year	per 1,000
1990	5.7
1991	5.6
1992	5.5
1993	5.6
1994	5.7
1995	5.8
1996	5.8
1997	5.8
1998	5.8
1999	5.8
2000	5.8
2001	5.8
2002	5.8
2003	5.8
2004	5.8
2005	5.8
2006	5.7
2007	5.7
2008	5.8
2009	5.8
2010	5.8
2011	5.9
2012	6
2013	6.2
2014	6.3
2015	6.4
2016	6.3
2017	6.1
2018	5.8
2019	5.5
2020	5.2
2021	4.9
2022	4.7