Year	Number
1961	7.922374429223744
1962	12.557077625570775
1963	18.2648401826484
1964	22.831050228310502
1965	28.538812785388128
1966	33.10502283105023
1967	39.1705069124424
1968	43.77880184331797
1969	49.76851851851852
1970	55.55555555555556
1971	62.33796296296297
1972	69.44444444444444
1973	76.62037037037037
1974	83.37182448036951
1975	90.5311778290993
1976	97.6905311778291
1977	104.3778801843318
1978	111.52073732718894
1979	118.66359447004609
1980	125.47126436781608
1981	123.18181818181819
1982	119.55555555555554
1983	117.58241758241759
1984	115.43478260869566
1985	113.33333333333333
1986	111.48936170212767
1987	109.47368421052633
1988	107.5
1989	104.48979591836735
1990	102.00400801603206
1991	101.14228456913827
1992	106.80000000000001
1993	112.79999999999998
1994	118.9
1995	124.4
1996	130
1997	133.92156862745097
1998	137.21153846153845
1999	141.50943396226415
2000	147.1897810218978