Year	per 1,000
1990	13.5
1991	14.5
1992	15.5
1993	16.7
1994	18
1995	19.3
1996	20.7
1997	22.1
1998	23.5
1999	24.9
2000	26.1
2001	27.2
2002	28
2003	28.4
2004	28.3
2005	27.8
2006	26.8
2007	25.4
2008	23.8
2009	22.1
2010	20.4
2011	18.8
2012	17.5
2013	16.4
2014	15.5
2015	14.8
2016	14.2
2017	13.8
2018	13.5
2019	13.3
2020	13.1
2021	13.1
2022	13.1