Year	per 1,000
1990	25.2
1991	24.9
1992	24.6
1993	24.3
1994	23.9
1995	23.6
1996	23.3
1997	22.9
1998	34.1
1999	30.1
2000	21.8
2001	21.4
2002	21
2003	20.6
2004	20.1
2005	19.6
2006	19.1
2007	18.6
2008	18.1
2009	17.6
2010	17.1
2011	16.7
2012	16.2
2013	15.8
2014	15.4
2015	15.1
2016	14.8
2017	14.5
2018	14.2
2019	13.9
2020	13.6
2021	13.4
2022	13.1