(Brian Snyder -- Reuters)

One of the hard things about writing about Mitt Romney's tax plan is that no one really knows what it is. The cuts are well-specified, but they cost $480 billion in 2015 alone, or close to $5 trillion over 10 years. Romney says he'll make up the difference by cutting tax breaks. It's not clear that's possible, but more to the point, Romney hasn't specified how he'd cut breaks. He flirted with a $17,000 cap on deduction, and, as Suzy reports, has now upped that number to $25,000 or $50,000, but has only said that's a possibility, not his actual plan. At any rate, none of those policies are likely to bring in enough revenue to pay for his plan.

But that ambiguity could give him an electoral boost. The political scientists Michael Tomz and Robert van Houweling, of Stanford and Berkeley respectively, have found that vagueness is actually an asset for political candidates.*

Tomz and van Houweling conducted an experiment where they asked 1,001 people for their views on government services. The respondents were given seven choices: increase services by a large, medium, or small amount; decrease services by a large, medium, or small amount; or keep them at the current level.

They were then asked to choose between four pairs of candidates; half were given the candidates' parties, and the other half weren't. The two pairs included a specific candidate, who took one of the seven specific positions on government services (increase/decrease, large/medium/small), and a vague candidate, who supported a range of positions like "increase services" (without specifying by how much) or "increase or decrease services a small amount or do nothing."

The last two pairs were the same as the first two, but with the vague candidate's position made more precise. For example, the candidate who wanted to "increase services" was altered to want to "increase services a medium amount", and one who wanted a "small increase or decrease or no change" was altered to just wanting "no change".

Tomz and van Houweling then measured if respondents were likelier to support a candidate in the first two rounds, when she's described vaguely, or the last two, when she's described precisely. They found that ambiguity helps across the board. It increases support by members of one's own party by 5.3 percentage points. No statistically significant change was found in support from independents or members of the other party; indeed, the midpoints were a 1.7 point bounce from independents and no change among members of the other party:

Source: Tomz and van Houweling

The effects are even bigger in "close calls" where the two candidates are equidistant or nearly equidistant from the voter, with candidates getting an ambiguity boost of 10.2 points from members of their own party in that situation, with no change in independents or the other party's voters.

Now, this is an experimental study, rather than an examination of actual campaigns. So its validity outside of a telephone survey is fair to question. But it does suggest that Mitt Romney will get a boost, especially among fellow Republicans, for not spelling out his tax plan. 

* Thanks to Kevin Collins for the pointer.