Comparison between ethnic heterogeneity and democracy, controlling for GDP

	Level of Heterogeneity
Low GDP	Low	Med	High
Democratic	53.33	59.09	53.66
Non-Democratic	46.67	40.91	46.34
High GDP	Low	Med	High
Democratic	9.68	21.43	60
Non-Democratic	90.32	78.57	40

Is the relationship between ethnic heterogeneity and democracy, controlling for GDP, spurious, additive or interactive?

Please make specific reference to the numbers in the table.