Year	per 1,000
1990	26.6
1991	24.9
1992	24.6
1993	25.1
1994	49.7
1995	24.1
1996	24.2
1997	23.1
1998	22.5
1999	22.7
2000	21
2001	20.2
2002	19.5
2003	18.7
2004	18
2005	17.4
2006	16.9
2007	16.3
2008	16.1
2009	15.5
2010	15.2
2011	15.1
2012	15.9
2013	15.7
2014	15.3
2015	15.5
2016	15
2017	14.8
2018	14.8
2019	14.2
2020	13.8
2021	13.6
2022	13.4