Year	Number
1961	0.43655699177250606
1962	0.59469941822883
1963	0.696429796848522
1964	0.8096599443216453
1965	0.9220765616222868
1966	1.1302849055274775
1967	1.204566396199139
1968	1.2901501367424755
1969	1.3435755952117192
1970	1.609130834668795
1971	1.7919981137826415
1972	2.074069233659517
1973	2.0872825117530573
1974	2.419265306122449
1975	2.526687428181258
1976	2.700003312684268
1977	3.2189387873935513
1978	3.510737803052978
1979	3.754847986075638
1980	3.859442196374458
1981	4.317411760150245
1982	4.361537591006828
1983	4.450778173635852
1984	4.282805946050299
1985	4.237145075795942
1986	4.023918670284092
1987	4.18206504775579
1988	4.253194211118474
1989	4.383498431058881
1990	4.3850018747656545
1991	4.318848498792131
1992	4.692745179636566
1993	4.727423739051646
1994	4.763861283336794
1995	4.7005234120809165