Year	Percent
1964-01-01	17.6634
1965-01-01	17.7981
1966-01-01	19.8120
1967-01-01	22.1624
1968-01-01	24.8173
1969-01-01	27.5349
1970-01-01	29.2786
1971-01-01	31.5571
1972-01-01	33.0405
1973-01-01	33.7277
1974-01-01	34.2159
1975-01-01	33.4580
1976-01-01	34.1705
1977-01-01	35.4815
1978-01-01	35.8811
1979-01-01	35.5726
1980-01-01	34.0359
1981-01-01	37.5404
1982-01-01	41.0458
1983-01-01	42.1968
1984-01-01	43.4576
1985-01-01	46.2225
1986-01-01	51.2441
1987-01-01	47.6776
1988-01-01	42.3933
1989-01-01	44.7526
1990-01-01	58.3568
1991-01-01	71.9150
1992-01-01	74.4880
1993-01-01	71.2939
1994-01-01	66.3722
1995-01-01	62.7575
1996-01-01	62.0572
1997-01-01	60.0800
1998-01-01	58.1895
1999-01-01	57.4603