Year	Number
1981	25.92058
1986	27.03864
1987	27.0805
1988	27.07743
1989	25.13168
1991	21.937
1992	21.27295
1993	21.06902
1994	21.26738
1995	21.56186
1996	20.0177
1997	19.56463
1998	19.31792
1999	18.71259
2000	18.5625
2001	18.07554
2002	17.44205
2003	17.49461
2004	17.47659
2005	16.9932
2006	16.80541
2007	16.54133
2008	15.86022
2009	15.8262
2010	16.1126
2011	17.36674
2012	17.56015
2015	18.90704
2016	19.32759
2017	19.33481