Year	Ratio
1970-01-01	0.422470003366470
1971-01-01	0.439069986343384
1972-01-01	0.468019992113113
1975-01-01	0.501169979572296
1976-01-01	0.485419988632202
1978-01-01	0.557510018348694
1979-01-01	0.582799971103668
1980-01-01	0.547999978065491
1998-01-01	0.649879992008209
1999-01-01	0.749459981918335
2000-01-01	0.736410021781921
2006-01-01	0.923629999160767
2008-01-01	0.911199986934662
2009-01-01	0.896369993686676
2011-01-01	0.915650010108948
2014-01-01	0.920350015163422
2015-01-01	0.904540002346039