Year	Number
1972	26.29379
1973	31.10512
1975	33.10022
1976	30.60287
1977	31.44598
1978	31.42424
1979	30.75058
1980	30.42529
1981	29.9396
1982	30.74667
1983	30.04857
1984	28.01274
1985	29.21739
1986	28.54604
1987	29.1033
1988	29.52288
1989	28.24655
1990	28.61673
1991	29.21201
1992	29.3945
1993	30.38361
1994	30.99631
1995	27.27083
1996	23.60519
1997	24.20083
1998	24.38472
1999	24.66093
2000	31.66522
2001	23.63404
2002	22.43788
2003	26.50671
2004	24.66193
2005	24.6682
2006	26.5462
2007	24.6698
2008	24.9969
2014	26.37134
2016	25.73171
2017	25.48855