Year	per 1,000
1990	3.7
1991	4.1
1992	4.5
1993	4.9
1994	5.3
1995	5.8
1996	6.2
1997	6.6
1998	6.9
1999	7.1
2000	7.2
2001	7.3
2002	7.4
2003	7.6
2004	7.8
2005	8
2006	8.3
2007	8.5
2008	8.9
2009	9.2
2010	9.5
2011	9.8
2012	10.1
2013	10.3
2014	10.5
2015	10.7
2016	10.7
2017	10.7
2018	10.7
2019	10.6
2020	10.5
2021	10.3
2022	10.2