Year	per 1,000
1990	39.5
1991	41.2
1992	42.6
1993	66.9
1994	44
1995	44
1996	43.6
1997	42.8
1998	41.9
1999	40.5
2000	38.6
2001	36.3
2002	33.4
2003	30.2
2004	27.1
2005	24
2006	21.3
2007	19
2008	17.3
2009	15.9
2010	14.9
2011	14.2
2012	13.7
2013	13.3
2014	13.1
2015	12.9
2016	12.6
2017	12.4
2018	12.1
2019	11.7
2020	11.4
2021	11
2022	10.7