Year	Number
1961	13.339746625621595
1962	14.142270049283754
1963	15.023744163612834
1964	15.862426693201787
1965	16.49162959478883
1966	17.478509279073297
1967	18.803815054166275
1968	19.880732756387005
1969	21.090443219722943
1970	21.899897222691475
1971	23.80555677956656
1972	25.416704221507466
1973	27.84665838404014
1974	30.170724138754142
1975	32.6613112754845
1976	35.29944149471699
1977	38.33811882499404
1978	40.98207446808511
1979	44.0097836401971
1980	45.82747855315573
1981	50.23260597897297
1982	52.48689062263409
1983	55.73878212479543
1984	59.17125120300701
1985	62.81238574983374
1986	67.46125576017596
1987	70.96848669050529
1988	75.29237601009918
1989	81.09685409906895
1990	85.29443549868695
1991	88.3818443811442
1992	93.07793879936045
1993	94.48486990818596
1994	95.5767414208704
1995	99.86444107955494
1996	104.93434737597052
1997	111.36738688280016
1998	115.07302664847182
1999	120.44445323069826
2000	124.45661483812997