Year	per 1,000
1990	27.3
1991	27.3
1992	27.3
1993	27.2
1994	27.2
1995	27.1
1996	26.9
1997	26.7
1998	26.4
1999	26
2000	25.5
2001	25
2002	24.4
2003	23.7
2004	22.9
2005	22.1
2006	21.2
2007	20.3
2008	19.4
2009	18.5
2010	17.7
2011	16.8
2012	16.1
2013	15.4
2014	14.8
2015	14.3
2016	13.8
2017	13.4
2018	13
2019	12.7
2020	12.4
2021	12.1
2022	11.8