Year	Number
1961	20.9009009009009
1962	21.8018018018018
1963	22.702702702702705
1964	23.603603603603602
1965	24.504504504504503
1966	25.405405405405407
1967	26.21184919210054
1968	27.01252236135957
1969	27.857142857142858
1970	28.685612788632326
1971	29.307282415630553
1972	30.353982300884958
1973	30.721830985915492
1974	31.140350877192986
1975	31.687719298245614
1976	31.18135593220339
1977	35.396321070234116
1978	37.9529921653609
1979	40.7822445561139
1980	40.580808080808076
1981	41.51269035532995
1982	41.85374149659864
1983	40.55042735042735
1984	50.96048109965636
1985	56.3034188034188
1986	55.23877917414721
1987	40.8503709064592
1988	41.03479853479853
1989	40.97592592592593
1990	46.98632702753325
1991	65.89977645305514
1992	68.33817653468944
1993	82.98767222625091
1994	163.0783308931186
1995	181.04201369609476
1996	197.15700396110913
1997	203.7526464361327
1998	213.35762623633525
1999	243.08333333333331
2000	262.4935483870968