Year	Number
1961	3.8
1962	5
1963	6.2
1964	7.3999999999999995
1965	8.6
1966	10.693069306930694
1967	12.871287128712872
1968	15.049504950495049
1969	24.15841584158416
1970	48.13725490196079
1971	53.333333333333336
1972	81.47058823529412
1973	96.56862745098039
1974	125.82524271844659
1975	140.19417475728156
1976	157.47572815533982
1977	171.747572815534
1978	185.5769230769231
1979	233.65384615384616
1980	267.40384615384613
1981	296.5740740740741
1982	291.2962962962963
1983	329.0740740740741
1984	363.51851851851853
1985	390.6542056074767
1986	406.48148148148147
1987	426.7889908256881
1988	429.63636363636357
1989	430.990990990991
1990	442.2018348623853
1991	457.54716981132077
1992	469.7115384615385
1993	473.0769230769231
1994	476.4423076923077
1995	451.5315315315315
1996	499.81308411214957
1997	564.4761904761905
1998	716.0714285714286
1999	720.3030303030303
2000	737.2549019607843