Year	per 1,000
1990	48
1991	46.8
1992	45.6
1993	44.3
1994	43
1995	41.7
1996	40.3
1997	38.9
1998	37.4
1999	36
2000	34.5
2001	33.2
2002	31.9
2003	30.8
2004	29.7
2005	28.7
2006	27.7
2007	26.9
2008	26.1
2009	25.4
2010	24.8
2011	24.3
2012	23.8
2013	23.3
2014	22.9
2015	22.5
2016	22.1
2017	21.8
2018	21.4
2019	21
2020	20.6
2021	20.2
2022	19.7