Year	Number
1973	24.81818
1975	18.78723
1989	22.4007
1990	21.6722
1991	20.73557
1992	20.66723
1993	20.14951
1994	20.13261
1995	19.55232
1996	19.87341
1997	17.88553
1998	18.23457
1999	18.54967
2000	18.6185
2001	18.35519
2002	18.19403
2003	19.29611
2004	18.49218
2005	18.66298
2006	18.30117
2007	20.78976
2009	18.16438
2010	18.53158
2011	17.76772
2012	16.78486
2013	15.73945
2014	18.77004
2015	23.35983
2016	29.27323