There are several ways one can go about determining which party's policies tend to perform better economically. One option is to look at what economists say. Another is to look at how the economy has performed during times when one party has had more power and compare that to how the economy has performed in the same place during times when the other party has had more power. A third way is to look at how the economy performs in places where one party tends to have more power compared to how the economy performs in places where the other party has more power. All three approaches have their advantages and disadvantages, but by weighing all three, one can potentially get a pretty decisive answer.
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In terms of specific policies, economists appear to consistently and overwhelmingly either support the Democrats' policies or to be to the left of the Democrats. This stance on policy issues unsurprisingly translates into which party economists support: Democratic economists outnumber Republican economists by 2.5 to 1. In 2012, economists felt that President Obama had a better grasp of economics than Mitt Romney by a margin of almost 2-to-1 and that President Obama would grow the economy faster than Mitt Romney by a a margin of 20 points
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The success of the Democratic states seems to play out across the board, even beyond the economic realm, as is evidenced by the consistently stronger performance of the Democratic states in terms of standard of living. In fact, even lifespans differ dramatically between red and blue states.
It seems clear that liberal policies are performing better at the state level across the board. I posted some ideas about why Democratic states are doing so much better economically earlier, but for our purposes here all that matters is that they are in fact doing so much better.
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No matter how one looks at the data- by relying on the findings of economists, by looking at state level or looking a federal data, and no matter which economic measure one looks at, the answer is the same: Democratic policies are performing better. And not just a little better- drastically better.