Year	Number
1961	3.368652752775946
1962	3.6890160203331592
1963	3.8342926914355484
1964	4.022968595728464
1965	4.249475277844682
1966	4.5982127088410865
1967	4.867262088081306
1968	5.188763221279715
1969	5.5845692090395485
1970	6.0244357120824
1971	6.054473062316668
1972	6.5822564082692345
1973	7.482813740065503
1974	7.791662456353082
1975	8.243067396571838
1976	8.604749504796244
1977	9.071760085683684
1978	9.190653924820023
1979	9.606775000433258
1980	10.034128124102269
1981	10.43673502285576
1982	10.989216826652916
1983	11.189271149944958
1984	11.385781886110053
1985	11.863310357885057
1986	12.28229252702266
1987	12.885627809269236
1992	20.568080765810535
1993	20.9450709318264
1994	21.891801057567804
1995	21.84360716389186