Year	Ratio
1970-01-01	0.545809984207153
1972-01-01	0.368250012397766
1976-01-01	0.415329992771149
1977-01-01	0.573719978332520
1979-01-01	0.555090010166168
1980-01-01	0.585500001907349
1981-01-01	0.605729997158051
1990-01-01	0.638909995555878
1991-01-01	0.754880011081696
1992-01-01	0.638670027256012
1993-01-01	0.710979998111725
1996-01-01	0.979659974575043
1999-01-01	0.870519995689392
2000-01-01	0.896920025348663
2002-01-01	1.154999971389770
2004-01-01	1.070700049400330
2005-01-01	1.056980013847350
2006-01-01	0.975969970226288
2011-01-01	1.031149983406070
2013-01-01	1.043400049209590