Year	Number
1971	23.41935
1972	21.34986
1973	20.89831
1974	20.7659
1975	21.28923
1977	17.68449
1978	20.26959
1979	22.75191
1980	22.84733
1981	19.01923
1982	18.03988
1983	17.85714
1984	17.5
1985	17.46926
1995	12.87689
1997	12.30753
2001	9.25187
2002	8.95985
2003	8.90328
2004	8.58929
2005	8.33625
2006	8.25044
2010	7.35691
2011	8.94444
2012	9.82751
2013	7.19372
2014	6.72131
2015	10.4196