The Boston/Manchester media market has topped the list for presidential TV advertising so far this year, costing an estimated $31.3 million for 18,882 airings, according to a new report released Tuesday.

In Iowa, candidates spent less, but got more for their money, About $28.6 million was spent in three Iowa media markets for 25,390 airings, according to the Wesleyan Media Project and Center for Responsive Politics report.

Overall, the volume of GOP presidential ads on the airwaves this election year is up by nearly 45 percent over the same period in 2011, but super PACs are even more dominant than they were in previous cycles.

These groups sponsored just 1 percent of ads to this point in 2007 and over two-thirds of ads in 2011, but they sponsored 81 percent from Jan. 1 through Dec. 9,  a 71 percent increase over 2011 and a 12,000 percent increase over 2007.

The findings are included in a new report from the Wesleyan Media Project, with which the Center for Responsive Politics partnered. The report shows that this year through Dec. 9, outside spending groups have sponsored 35,743 of 44,270 of the ads in the Republican primaries.

On the Democratic side, Hillary Clinton has double the ad total of her nearest competitor, Bernie Sanders (13,450 to 7,205). Martin O’Malley and former long-shot candidate Larry Lessig have aired very few ads.

Des Moines, Iowa, ranked second with just over 11,000 airings. Cedar Rapids, Iowa, was third with nearly 9,500 airings. Other early primary states receiving advertising are South Carolina and Nevada.

There’s a big disconnect, in most cases, between the amount of money spent advertising on a candidate’s behalf and how well that candidate is doing in the polls.

Former Florida Gov. Jeb Bush and the pro-Bush Right to Rise USA super PAC have aired more than 15,000 ads on broadcast television, national network and national cable television since Jan. 1, at a cost of almost $26 million.

Meanwhile, Donald Trump has aired no ads, and Ted Cruz has benefited from only 457 ads since the start of the year through Dec. 9.

Bush’s poll numbers are terrible, though, while Trump and Cruz have been surging.

Almost all of the advertising is coming from single candidate groups, and most of it is sponsored by groups that disclose who their donors are.

The main exception: Conservative Solutions Project, which has been the main group advertising in support of Sen. Marco Rubio (R-Fla.).

It is a 501(c)(4) “social welfare” group that doesn’t disclose the names of its donors — not a super PAC like virtually all of the other groups airing ads. It has been the second biggest spender in the race, after Right to Rise.

“It’s noteworthy that Conservative Solutions Project is spending far more than Rubio’s super PAC,” said Michael Franz, co-director of the Wesleyan Media Project. “Rubio is the only candidate who is being backed by a dark money sponsor to such a high degree.”

Conservative Solutions Project is an example of the single-candidate dark money group, a new breed that appeared in the 2014 elections. It is explained in our blog post about Carolina Rising and its support for now-Sen. Thom Tillis (R) in North Carolina.

Carolina Rising, it turned out, was funded almost entirely by the biggest of the politically active dark money groups, Crossroads GPS — which ranks No. 1 in each of the past several years in the percentage of its funds that have been spent on politics, according to a new tally by CRP. But where the money originally came from is unclear.

Read more here, and check out our webchat discussing the report.

Cost and Count of Ads Favoring Each Presidential Candidate (including supportive groups)

Table 7: Top Media Markets in Presidential Nomination Race by Airings