Year	per 1,000
1990	17.4
1991	18.3
1992	19.3
1993	20.4
1994	21.6
1995	22.9
1996	24.3
1997	25.7
1998	27.1
1999	28.4
2000	29.5
2001	30.4
2002	30.9
2003	31.1
2004	31
2005	30.6
2006	29.9
2007	29
2008	28
2009	26.9
2010	25.8
2011	24.6
2012	23.3
2013	22
2014	20.7
2015	19.6
2016	18.7
2017	18
2018	17.6
2019	17.3
2020	17
2021	16.8
2022	16.7