Year	Number
1961	20.37063314130034
1962	21.331664723114994
1963	22.434040864907757
1964	23.57867806235767
1965	24.717390699357136
1966	26.662094448954456
1967	30.44109047367102
1968	31.854258268686813
1969	33.50881598035934
1970	34.8088827203331
1971	35.200528273408445
1972	38.091005752610485
1973	40.30711794201003
1974	42.5116090712743
1975	45.46277530063505
1976	47.090865397452674
1977	48.82733619763695
1978	52.712606837606835
1979	57.67050629520493
1980	60.87145735392881
1981	65.46694525432673
1982	69.33550443274983
1983	73.32663208151314
1984	76.80358964718208
1985	83.4251346856984
1986	87.08902825235437
1987	89.29694941433904
1988	91.19161399722522
1989	89.9205466961052
1990	94.68484134646978
1991	97.37566931991627
1992	96.15363043072179
1993	101.28120772160896
1994	103.845235147401
1995	112.26647815912636
1996	111.92507026061229
1997	113.58133192428384
1998	115.21382018106628
1999	126.81375327233962
2000	153.97300964465143
2001	168.4430739363104