Year	per 1,000
1990	22.8
1991	22.2
1992	21.4
1993	20.6
1994	19.8
1995	19.1
1996	18.2
1997	17.4
1998	16.6
1999	15.7
2000	14.9
2001	14
2002	13.2
2003	12.3
2004	11.4
2005	10.6
2006	9.7
2007	8.8
2008	30
2009	7.1
2010	6.2
2011	5.5
2012	4.8
2013	4.1
2014	3.6
2015	3.2
2016	3
2017	2.8
2018	2.6
2019	2.5
2020	2.4
2021	2.2
2022	2.1