There's no shortage of ideas to make the world a better place. But if you asked a team of top economists to make a priority list of things that would do the most good per dollar spent, what would they say?

That's exactly what the influential Bjorn Lomborg, an adjunct professor at the Copenhagen Business School and director of the Copenhagen Consensus Centre,  has done. He asked a panel of 32 economists to assess the likely effectiveness of 169 global "sustainable development goals" currently being considered by the United Nations.

The proposals were ranked in four groups from the best – those that would do more than 15 times as much economic, social, and environmental good as they cost - to the worst ,which are likely to cost more than they yield in benefits.

Some would be phenomenal. Every dollar spent on reducing malnutrition, for example, can do $45 worth of good over time. The benefit derived from every dollar spent on preventing malaria yields $35 and a dollar spent providing modern cooking fuels delivers $15.

But the economists were not impressed by all the proposals - at least nine of the targets being debated by the UN were deemed to be poor.

"Not all targets are equally worthwhile," said Lomborg, who was in Australia for the recent G20 meeting.

"Some things can do an amazing amount of good at fairly low cost but others are not so smart."

Lomborg's aim is to influence the crucial negotiations now taking place at the UN. An array of expert panels, working groups and researchers has been busy coming up with proposals for a list of "Sustainable Development Goals" that will shape international co-operation over the next 15 years. A special "My World" survey asked five million people (including Australians) their views,  and an "Open Working Group", involving 70 nations, was set up last year to come up with a list of global priorities. It has proposed 17 goals and 169 targets covering everything from malnutrition, tobacco control and sustainable tourism to renewable energy.

The trigger  for this bout of international priority-setting is the looming conclusion of the Millennium Development Goals adopted by world leaders in 2000. The MDGs, as they are known, was an eight-point plan to reduce extreme poverty and hunger; get children, especially girls, into school; ensure access to water and sanitation; improve the health of mothers and children, fight disease and protect the environment, all by December 31, 2015. They included very specific targets - the first was to halve the proportion of people living on less than $1.25 a day. British development expert, David Hulme, called the MDGs "the world's biggest promise".

Not all the goals will be achieved. The second – universal primary education – seems well out of reach, although things have improved. Primary enrolments in developing regions are now over 90 per cent compared with 82 per cent in 1999. And the good news is that some goals were achieved much more quickly than expected. The target to halve poverty was reached five years ahead of schedule, thanks largely to the rapid economic advance of China. Safe water is another MDG success story. In 1990 – the baseline for the goals - around 30 percent of people in the developing world lacked access to a reliable source of clean water. That's on track to have shrunk to 11 per cent by the end of next year. Maternal, child and infant mortality rates in the developing world have also plunged. In 1990 about 12 million children died annually before reaching their fifth birthdays. Now it's fewer than seven million. The proportion of chronically hungry people, almost 24 per cent in 1990, is expected to be down to 12.2 per cent by the end of 2015.

It's likely the MDGs played a significant role in those achievements by firing up public support across the world.

"The MDGs have been extraordinarily important," says World Vision chief, Tim Costello, "They were an historic galvanising of international focus on the poor."

Costello does not consider the unmet goals a failure.

"For the first time we know where we are off target," he says. "It shows how far we've come and how far we've got to go."

In a speech at Harvard University this week the UN Secretary-General Ban Ki-moon said the new set of sustainable development goals was "taking shape".

"We are determined to finish the job of the MDGs," he said. "But we also want to address emerging issues such as inequality. And we want the new goals to include critical factors that were not part of the MDG framework, such as building peaceful societies with responsive, accountable institutions."

Ban says the new goals will be universal in scope and adaptable to each country.

New themes, such as upgrading urban slums, have been proposed. Martin Thomas, the chief of Habitat for Humanity Australia, a housing provider for low-income families, says this is crucial because the uncontrolled growth of slums in Asia "looms as one of the greatest development challenges of the 21st Century".

But the pithiness of the MDGs is proving difficult to replicate. A host of governments, experts, interest groups and NGOS have pushed for a much bigger list of goals and targets for the next 15 years.

Many are worried whatever replaces the MDGs will be too unwieldy.

"Everyone is having a say, and at one level that's good," says Costello.

"But the new goals won't galvanise anyone unless they are sharper, fewer and clearer."

Lomborg says the process to set new global goals has the potential to create one of the world's "most powerful policy documents" and influence $2.5 trillion in development aid spending.

"It's a phenomenal idea - when do we get the chance to talk about what the world should do for the next 15 years," he says.

But Lomborg wants the UN to be hard-headed- his economic analysis shows the goals chosen should maximise the chances that the money allocated to achieve them is well spent.

"Lots of things haven't worked at the UN but we know one thing has - the MDGs," he said. "So it's safe to say there should be a similar number of goals again – we certainly should not have 169 targets."

Lomborg admits some of the conclusions of his cost-benefit analysis are "unnerving." Combating HIV/AIDS, for example, was not ranked among the effective targets. Because drugs to treat HIV/AIDS are relatively expensive and treatment lifelong, preventing a single HIV fatality costs the same as saving 10 people from dying of malaria.

But Lomborg acknowledges money isn't the only important consideration.

"Just because champagne is expensive doesn't mean it isn't worth paying for," he says.

However he points out that getting the best possible goals onto the global agenda could be "the best thing any of us gets to do this decade".

Ban Ki-moon, now has the tricky task of negotiating the new set of goals to be ratified by world leaders next September. Lomborg says the UN chief needs to depart from his typical caution and deliver a limited set of goals that will make a difference. Of course, international politics will ultimately determine the final list. But small improvements could have a big effect.

"If we could just get rid of one bad goal and get one good target in there...it could achieve a lot of good," says Lomborg.

"When trillions of dollars are at stake, even small adjustments can make a world of difference."