Year	per 1,000
1990	29.7
1991	29.3
1992	28.8
1993	28.3
1994	27.7
1995	27.2
1996	26.5
1997	25.9
1998	25.2
1999	24.4
2000	23.7
2001	22.8
2002	22
2003	21.3
2004	20.5
2005	19.8
2006	19.1
2007	18.4
2008	17.8
2009	17.2
2010	16.6
2011	16.1
2012	15.7
2013	15.5
2014	15.5
2015	15.5
2016	15.5
2017	15.5
2018	15.5
2019	15.5
2020	15.5
2021	15.5
2022	15.5