Year	gross (GPI)
1978	0.851960003376007
1979	0.857379972934723
1980	0.860729992389679
1981	0.861980020999908
1982	0.872479975223541
1983	0.883899986743927
1984	0.886919975280762
1985	0.872330009937286
1986	0.888830006122589
1987	0.940509974956512
1992	0.951799988746643
1993	0.946860015392303
1994	0.946340024471283
1995	0.945540010929108
1996	0.944630026817322
1997	0.947570025920868
1998	0.971029996871948