Year Percent 1969-01-01 0.1591176 1970-01-01 0.3217641 1971-01-01 0.5085180 1972-01-01 0.6739795 1973-01-01 0.7631886 1974-01-01 0.8137840 1975-01-01 0.6537458 1976-01-01 0.7918305 1977-01-01 0.7875305 1978-01-01 0.7866780 1979-01-01 0.9473372 1980-01-01 1.0496120 1981-01-01 1.0482590 1982-01-01 1.1666770 1983-01-01 1.2929890 1984-01-01 1.3598610 1985-01-01 1.3333430 1986-01-01 1.4315190 1987-01-01 1.6379540 1988-01-01 1.9991320 1989-01-01 2.2460160 1990-01-01 2.0189530 1991-01-01 1.6783440 1992-01-01 1.1808500 1993-01-01 1.0568340 1996-01-01 0.8798108 1997-01-01 0.6868176 1998-01-01 0.7809177 1999-01-01 0.8953087 2000-01-01 0.9093925 2001-01-01 0.8509588 2002-01-01 0.8538731 2003-01-01 0.8441362