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Political Science
POL 51
Ben Highton

5614Pol 51 Lecture 9Expanding our Theory of Presidential Election OutcomesStronger Econ causes higher IncVoteWhy does Econ cause IncVoteas the Econ gets better voters provide more support for the incumbent party as the Econ gets worse then the support for the incumbent party decreasesOne possibility suppose voters respond to how positive or negative meda coverage Media of the presidents party is Wwhen the economy is stronger media coverage becomes more positive When the economy is weaker media coverage is more negative In other words Econ X causes Media Z and Media Z causes IncVote YWe call Media an intervening variable in the EconIncVote causal relationshipWhat would happen to the EconIncVote correlation in we control for Media the correlation would dissapear but we would not conclude that X does not cause YWhat would happen if the economy got stronger but for some reason media coverage did not become more positivewe would not expect a larger IncVote If the explanation for why X causes Y is Z then if X changes but Z does not we would not expect Y to changeConfounding and Intervening Variablesconsider an XY causal hypothesisZ is an intervening variable if X causes Z and Z causes Y In this case the XY correlation dissapears when we control for Z But this does not mean that X does not cause YZ is a confounding variable if Z causes X and Z causes YZ is a confounding variable is Z is correlated with X and Z causes Y and Z is not caused by Xin the case of an intervening variable i
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