Assumes revenue neutrality
In his simulation leading to the 5.4 percent growth estimate Diamond assumes that the Romney tax plan is revenue neutral. Yet Rosen is using the Diamond growth estimate to show that the plan can be revenue-neutral. Therefore the argument is circular.
This point was made by Dylan Mathews in a blog post. The relevant excerpt from the Diamond paper is also cited below.

According to Dylan Mathews the problems 
CONTEXT(Help)
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Visualizing the Romney Tax Debate »Visualizing the Romney Tax Debate
Romney's plan stated »Romney's plan stated
But does it compute? »But does it compute?
No - it does not compute »No - it does not compute
The TPC case »The TPC case
Growth effect claim »Growth effect claim
Ignores growth potential »Ignores growth potential
Growth-supportive studies »Growth-supportive studies
1. Rosen »1. Rosen
Growth estimate 1 - Diamond study »Growth estimate 1 - Diamond study
Objections to Diamond »Objections to Diamond
Assumes revenue neutrality
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