Year	Number
1971	48.49985
1972	47.16564
1973	44.34221
1974	46.11343
1975	46.03242
1976	44.3135
1977	44.9922
1978	39.67265
1979	47.37794
1980	59.0234
1981	63.94322
1982	62.7242
1983	59.297
1984	53.56085
1985	49.96845
1986	48.0888
1987	48.27671
1988	49.38413
1989	43.27498
1990	40.67554
1991	36.07524
1992	30.17056
1993	26.61047
1994	30.15261
1995	32.7529
1996	37.89781
1997	43.198
1998	46.51484
2000	67.33913
2008	62.28293
2009	57.9406
2010	54.05852
2011	55.06929