Year	per 1,000
1990	32.5
1991	31.3
1992	30.3
1993	29.3
1994	28.3
1995	27.4
1996	26.6
1997	25.6
1998	24.6
1999	23.6
2000	22.5
2001	21.5
2002	20.5
2003	19.5
2004	18.6
2005	17.8
2006	17
2007	16.3
2008	15.6
2009	14.9
2010	14.2
2011	13.6
2012	13
2013	12.5
2014	12.1
2015	11.8
2016	11.6
2017	11.4
2018	11.2
2019	13.5
2020	11
2021	10.8
2022	10.7