Measuring stimulus

In this post, I disagreed with Menzie Chinn and argued that CBO estimates of the impactof the stimulus are not estimates. Charles Steele writes in a comment:

CBO's approach *is* an analysis of what stimulus actually did; such analysis necessarily requires a counterfactual, based on an underlying model of what would have happened otherwise.

So while we might disagree with the neoKeynesian underpinnings, this is an argument about the best macro model. So… what's your alternative model? And could...