Deb Matthews has been given the most important and the most challenging posting in Ontario's cabinet. But she can't stop talking about her old job.

"I always draw on my experience from Health," she said during an interview this week. Repeatedly returning to the subject, Ms. Matthews made no bones about viewing her new role as the president of the treasury board through the lens of five years running the province's biggest ministry.

This is not a stubborn refusal to move on; it is the biggest reason, beyond her close working relationship with Premier Kathleen Wynne, she has been tasked with quarterbacking the elimination of a $12.5-billion deficit in a three-year span.

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Defying predictions, she succeeded in flattening annual increases in health costs – which, because of an aging population and insatiable demand for new and expensive treatments, were threatening to eat the provincial budget whole – at roughly 2 1/2 per cent. Whether the skills that enabled Ms. Matthews to do so prove applicable across the rest of government will do much to determine whether Ms. Wynne is able to achieve her goal of returning to balance without significantly raising taxes or tearing social programs to shreds.

The first such test will come with labour negotiations that Ms. Matthews is now expected to spearhead. For a flag-bearer of her party's left flank, she proved surprisingly hard-edged and effective while at Health in reducing the amount the province pays to its pharmacists, and winning major concessions from doctors. But those are professions with which her Liberals have little natural alliance, and the same can't be said for teachers, whose contract negotiations before year's end will be both hugely important to the province's bottom line and a stage-setter for talks with other unions.

In the interview, Ms. Matthews reiterated that, as with other workers in the broader public sector, teachers will be expected to accept "net zeroes" in compensation increases. But as she was more circumspect on whether the government will also seek to use the negotiations to drive workforce reductions or changes to job descriptions, it appeared the appetite for structural change that she displayed in Health is likelier to manifest itself in other ways.

One of those is the belief that, rather than trying to micromanage the hunt for efficiencies, it's best to leave service providers to make do with less than they think they need – something the government has done, to a large extent, with hospitals.

"If there's more money every year, you'll do more of the same thing and you won't take the time to say, 'Whoa, is there a better way to do it?'" she said. "I think some of the improvements in Health have come because the purse strings are tighter."

She also hinted at meeting the needs of growing suburban populations, which could drive up costs in various ministries, with what could be a controversial reallocation from small-town and rural areas that are overserved by comparison.

That's already begun with hospitals, she noted, and is now spreading to child care and other social services. "Some will get more, and some will get less, and that's what happens when you start to do this without increasing the size of the pie."

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Then there is the idea, pivotal to health reforms of recent years, that to find efficiencies and improve outcomes it is necessary to focus on the small segment of the population that makes disproportionate use of services.

In health care, that's meant more aggressive and integrated case management of the sorts of people who turn up frequently in emergency rooms. To apply that more pro-active approach to "people with mental-health issues and intersection with the justice system, or kids in care of the Children's Aid Society," would by Ms. Matthews' estimate improve cost efficiency.

Not that she's under any illusion that even the file on which she spent a half-decade is where it needs to be.

"You look at how our health-care system stacks up against other health-care systems, we've got really good outcomes for patients, but we don't have a health-care system that's high-performing," she said. "We've got way too many people going to emergency departments when they don't need to. It's way too hard to get an appointment with a family doctor – same day, next day, when you're sick. There's a lot we can do that is better for patients and better value for money."

She added that Eric Hoskins, her replacement at Health, will be on top of that now. That he'll have Ms. Matthews breathing down his neck won't set him apart from anyone else around the cabinet table.