Year	Number
1961	5.138135309697682
1962	5.456575571178342
1963	5.9335462900573805
1964	6.44599420383048
1965	6.978608310981636
1966	8.808594044487542
1967	10.542707587571513
1968	12.666719058380343
1969	14.521085249132826
1970	11.341497476401422
1971	13.216149811104671
1972	15.953781325567775
1973	18.931913341006144
1974	21.859584185827252
1975	26.34558371551627
1976	29.743061781284318
1977	34.56840217445555
1978	40.74913282093193
1979	48.01050581787474
1980	53.086408629098585
1981	56.096015665443005
1982	55.92918873673014
1983	56.004168230286076
1984	55.38255391869586
1985	53.51978838658384
1986	54.489875223143954
1987	55.22187456203139
1988	55.186376296714315
1989	54.410736263479315
1990	53.223972808453574
1991	53.16872931261382
1992	53.559687662227624
1993	53.79682501069696
1994	56.88003034746419
1995	58.20946207109805
1996	58.61558759777589
1997	62.01421232520573