Year	Number
1971	41.68144
1972	39.34343
1973	37.6848
1974	41.86643
1976	47.37831
1981	46.2144
1983	38.01422
1984	38.52209
1985	31.17927
1986	34.76276
1987	34.51549
1988	36.4305
1989	37.59977
1990	35.69737
1991	36.50326
1992	39.90338
1993	41.68662
1994	44.81117
1996	52.07361
1999	34.77068
2000	36.83793
2002	39.20075
2003	35.85763
2004	34.98787
2008	30.15332
2011	27.74673
2013	27.80796
2017	18.90138
2018	28.05781