Year	Number
1961	13.083679504719875
1962	14.017417985916582
1963	14.952962101343191
1964	15.87161405540833
1965	16.674826258892754
1966	18.2243142448459
1967	19.72327570138381
1968	21.21142996646996
1969	22.75404371913862
1970	22.951868065689983
1971	25.045490658181343
1972	27.23154286483991
1973	29.046871622084844
1974	31.670087720323252
1975	35.85417529819198
1976	38.49809279299948
1977	42.32196595518
1978	46.76433577764047
1979	51.370564524000194
1980	54.402118656010934
1981	58.51661119814754
1982	59.95817643223351
1983	62.14193783748675
1984	63.833942857204
1985	65.28456043674286
1986	68.13667892355296
1987	70.66936797681159
1988	73.3923276211404
1989	76.76275081430822
1990	79.07507727620892
1991	80.66967844192918
1992	90.8470725195352
1993	91.26422602531105
1994	91.22604774484024
1995	91.89163357754502
1996	92.8139324659623
1997	94.33970921095258
1998	96.05937432198996
1999	98.73296974833904