Year	per 1,000
1990	2.7
1991	2.8
1992	2.8
1993	2.9
1994	3
1995	3.1
1996	3.1
1997	3.2
1998	3.2
1999	3.1
2000	3.1
2001	3
2002	3
2003	2.9
2004	2.9
2005	2.8
2006	2.9
2007	3
2008	3.1
2009	3.1
2010	2.9
2011	2.7
2012	2.6
2013	2.5
2014	2.6
2015	2.8
2016	2.9
2017	3
2018	3
2019	2.9
2020	2.8
2021	2.8
2022	2.8