Year	Number
1971	36.56708
1972	34.84157
1973	32.81628
1974	32.60616
1975	33.55193
1976	33.08004
1977	33.43573
1978	31.43834
1979	31.15471
1980	30.98952
1981	31.06377
1982	32.06037
1983	32.16868
1984	33.1817
1985	34.78178
1986	30.56607
1987	28.74148
1988	28.86524
1989	27.8647
1990	25.81876
1991	26.76233
1992	26.40651
1993	23.05941
1994	22.5199
1995	22.36828
1996	21.84503
1997	22.171
1998	21.78031
1999	23.54249
2000	25.69749
2001	24.53753
2002	25.64829
2003	21.76544
2004	21.81863
2005	21.97287
2006	23.77022
2007	23.60062
2008	18.73722
2009	17.1785
2010	19.643
2011	18.66427
2013	15.91497