Year	Number
1961	2.8654316060007203
1962	3.1050692046542667
1963	3.1575991241848733
1964	3.346129117658182
1965	3.551058302776814
1966	3.956466192136634
1967	4.295884486206665
1968	4.584782937528362
1969	5.0071317117065375
1970	5.474819654941406
1971	5.492472773862908
1972	5.2226246621510715
1973	5.78239168467634
1974	5.905727134877331
1975	6.014738279589286
1976	5.967514847429858
1977	6.099072399060852
1978	6.122329372902126
1979	6.259799477361208
1980	6.428685026638747
1981	6.330365579377437
1982	6.3716455669035525
1983	6.34228017656908
1984	6.523284274430585
1985	6.3723357411698105
1986	6.371671033592742
1987	6.468684689543585
1988	6.099878332334831
1989	6.285378070915056
1990	6.204913627046809
1991	5.8240933828391235
1992	6.120314128530032
1993	6.4715605054680205
1994	6.90243911672402
1995	6.622487721620398