Year	per 1,000
1990	39.6
1991	39.1
1992	38.5
1993	37.9
1994	37.2
1995	36.6
1996	35.8
1997	35
1998	34.2
1999	33.3
2000	32.3
2001	31.3
2002	30.3
2003	29.4
2004	28.4
2005	27.5
2006	26.7
2007	25.9
2008	25.1
2009	24.3
2010	23.6
2011	22.9
2012	22.5
2013	22.2
2014	22.2
2015	22.2
2016	22.2
2017	22.2
2018	22.2
2019	22.2
2020	22.2
2021	22.2
2022	22.2