year nl us 1984 0.041 0.008 1985 0.062 0.041 1986 0.144 0.098 1987 0.333 0.164 1988 0.574 0.230 1989 0.754 0.303 1990 0.852 0.385 1991 0.902 0.475 1992 0.926 0.525 1993 0.943 0.590 1994 0.954 0.648 1995 0.959 0.721 1996 0.970 0.770