Year	per 1,000
1990	36.9
1991	36.1
1992	35.3
1993	34.3
1994	33.3
1995	32.3
1996	31.2
1997	30
1998	28.8
1999	27.5
2000	26.2
2001	24.8
2002	23.5
2003	22.3
2004	21.1
2005	19.9
2006	18.9
2007	17.9
2008	17
2009	16.1
2010	15.3
2011	14.6
2012	14.1
2013	13.8
2014	13.8
2015	13.8
2016	13.8
2017	13.8
2018	13.8
2019	13.8
2020	13.8
2021	13.8
2022	13.8