Year	Number
1971	20.56458
1972	27.12219
1973	25.76538
1975	18.69075
1976	21.76221
1977	25.40777
1978	25.55945
1979	27.66688
1980	27.60482
1981	27.47215
1983	28.34158
1986	28.33107
1987	29.69178
1988	28.37379
1989	29.28406
1990	26.4769
1991	25.94396
1992	23.41365
1993	22.95579
1994	18.99461
1995	11.4822
1996	12.15131
1997	12.2671
1998	13.08821
1999	24.62678
2000	26.33289
2001	25.70308
2002	26.30721
2003	26.96311
2004	27.61402
2005	24.14544
2006	29.01924
2007	29.03188
2008	25.27655
2009	24.16832
2010	24.51937
2011	26.25349
2012	27.17567
2016	32.98522
2017	33.33772
2018	33.14655