Year	Number
1986	25.67562
1989	22.62178
1990	20.66277
1991	19.78228
1992	19.34524
1993	18.85889
1994	19.0124
1995	20.34234
1996	21.49086
1997	22.61298
1998	22.21895
2001	18.7209
2002	18.89743
2003	18.50973
2004	17.93263
2005	17.26973
2006	16.77062
2007	16.5296
2008	16.63423
2009	16.40689
2010	16.24776
2011	16.35795
2012	16.19104
2013	16.48238
2014	16.85665
2015	16.2004
2016	18.5511
2017	20.75555
2018	19.63913
2019	17.21457