Dexter has said the province spent $85,000 on an untendered contract to have John Dalton, president of Power Advisory in Carlisle, Mass., determine whether getting electricity from Muskrat Falls would be cheaper than getting it from wind turbines, natural gas plants or hydro dams in Quebec.
He said work started on the assessment in September.
The opposition has been calling for an independent review for months, but the premier did not say anything about Dalton's work until Wednesday.
When asked why he kept the study under wraps, Dexter initially indicated he did not want the media pestering Dalton's company.
Then on Thursday, Dexter changed gears, saying outside the legislature that the only thing that mattered was that the work was being done.
"People want to be assured that this is going to lead to the lowest and fairest rates," he said.
When pressed for a more specific answer, Dexter said: "Usually, when we talk about (studies), it is when we have something that is of a nature that is mature enough to be able to talk about it. It takes time to develop that.
"They have to do the work, they have to do the research, they have to do the analysis. ... It's not a riddle. I'm not trying to be anything but forthright."
Dexter said he hasn't seen the results from the study.
Progressive Conservative Leader Jamie Baillie said he believes the premier chose to remain mute until he was sure the study would give him the answers he wanted — a charge Dexter has denied.
"He has determined what he wants the outcome to be, and he wants to make sure that's what it is before he releases the report," Baillie said outside the legislature as members gathered for the final sitting of the fall session.
"That just shows how backwards the decision-making around Muskrat Falls has been. To decide the outcome first and study later is exactly what is wrong with the approach the premier's taking."
Baillie suggested Dalton's work could hardly be considered independent because his company has close ties with the NDP government, having already completed extensive work on the province's renewable energy strategy.
During question period, the opposition Liberals and Conservatives questioned the premier's motives.
Dexter committed to releasing the terms of reference for the assessment, which he expects to release to the public next month before hearings begin on Muskrat Falls at the province's Utility and Review Board.
Those hearings will include discussion about the so-called Maritime link, the subsea electrical cable that will connect Nova Scotia with the Newfoundland and Labrador power grid. The link is estimated to cost $1.3 billion to $1.5 billion.
That portion of the project is supposed to be built by a subsidiary of Emera Inc., parent of Nova Scotia Power Inc., the province's privately owned electric utility.
Prime Minister Stephen Harper has signed off on a loan guarantee for Muskrat Falls, which is estimated to cost between $7.5 billion and $7.7 billion.