Year	per 1,000
1990	29.4
1991	28.4
1992	27.5
1993	26.6
1994	25.8
1995	24.9
1996	24.1
1997	23.3
1998	22.6
1999	21.9
2000	21.2
2001	20.6
2002	19.9
2003	19.3
2004	18.7
2005	18.2
2006	17.7
2007	17.2
2008	16.7
2009	16.3
2010	15.9
2011	15.5
2012	15.1
2013	14.8
2014	14.4
2015	14.1
2016	13.7
2017	13.4
2018	13.1
2019	12.7
2020	12.4
2021	12
2022	11.7