Table 5. Correlations of each decade’s concepts prominence values. Color intensity indicates the strength of correlation (green is positive and red is negative).

Decade	1960s	1970s	1980s	1990s	2000s	2010s
1960s	-	0.749	0.558	0.028	-0.458	-0.033
1970s		-	0.704	0.007	-0.663	0.064
1980s			-	0.225	-0.633	-0.124
1990s				-	0.196	-0.855
2000s					-	-0.556
2010s						-