Year	Number
1961	38.950019076688285
1962	42.20569437830522
1963	45.29183263247463
1964	47.96228658795549
1965	50.40906200127194
1966	52.30074000754148
1967	53.73999953621038
1968	54.98994509343155
1969	57.23433691284011
1970	59.67232222381052
1971	62.02315319181715
1972	62.902395866126774
1973	65.23541918182886
1974	66.15223560519216
1975	74.64974186027146
1976	74.59839539355137
1977	76.11565329378708
1978	79.82710689668305
1979	84.13345874610135
1980	86.97345130953066
1981	94.77215900620675
1982	94.71022414230369
1983	95.93149338257024
1984	97.63746602550701
1985	100.6140799988361
1986	107.07597256996536
1987	112.32728689230092
1988	118.69688214810377
1989	121.92858475124285
1990	125.2497611093001
1991	128.0634360849991
1992	129.0930429204572
1993	130.41891042126142
1994	132.04647095512553
1995	132.31515604141057
1996	135.04004099112856
1997	132.90046620871684