Year	per 1,000
1990	2.9
1991	2.9
1992	3
1993	3.1
1994	3.3
1995	3.4
1996	3.5
1997	3.7
1998	3.8
1999	3.9
2000	3.9
2001	4
2002	4
2003	4
2004	4
2005	3.9
2006	3.9
2007	3.9
2008	3.9
2009	3.8
2010	3.8
2011	3.9
2012	3.9
2013	4
2014	4.1
2015	4.3
2016	4.4
2017	4.5
2018	4.5
2019	4.5
2020	4.4
2021	4.3
2022	4.2