Year	per 1,000
1990	36.3
1991	35.1
1992	33.8
1993	32.7
1994	31.6
1995	30.5
1996	29.5
1997	28.6
1998	27.6
1999	26.8
2000	25.9
2001	25.1
2002	24.3
2003	23.5
2004	22.7
2005	22
2006	21.3
2007	20.6
2008	19.9
2009	19.2
2010	18.5
2011	17.9
2012	17.2
2013	16.6
2014	16
2015	15.4
2016	14.8
2017	14.3
2018	13.7
2019	13.2
2020	12.7
2021	12.3
2022	11.8