FOR its next 15-year global development agenda, the UN needs to get a fix on achievable goals. Economics may well show the way. If you could come up with goals for the world to aspire to over the next 15 years, what would they be? What should we focus on? The United Nations is conducting an online survey, asking people what matters most to them. Over 7 million people have responded, with everything from better transport and roads, to affordable and nutritious food, under consideration. So far, the top priority is better education, followed by better healthcare and job opportunities, with phone and internet access at the bottom. For the survey participants from Malaysia, education and an honest and responsive government comes first, while support for people who can't work and reliable energy at home rank last. But to make a more considered priority list, we need much more information on what solutions exist, their costs and their likelihood of success to make a better prioritisation. This survey is part of a larger effort by the UN to find a successor scheme for the Millennium Development Goals (MDGs) which expire at the end of this year. The MDGs set 21 mostly sharp and achievable targets in eight areas, including poverty and hunger, gender equality, education, and child and maternal health. These goals have been hugely successful, not only in driving more development funding but also in making the world better. For instance, the world promised to halve the proportion of starving people counting from 1990. And the progress has been remarkable. In 1990, almost 24% of all people in the developing world were starving. In 2012, "only" 14.5% were starving, and if trends continue, the world will reach 12.2% in 2015, just shy of the halving at 11.9%. Likewise, we promised to cut by half the proportion of poor. In 1990, 43% of the developing world lived below a dollar a day. In 2010, the proportion had already been more than halved at 20.6% – on current trends the proportion will drop below 15% by 2015, showing spectacular progress. The UN is working to replace the MDGs with a scheme called Sustainable Development Goals (SDGs). But that's easier said than done. Last month, 70 UN ambassadors in the open working group proposed a vertiginous 169 targets. Clearly we need priorities. The SDGs will determine a large part of the US$2.5 trillion (RM9.07 trillion) development aid the world will spend until 2030. To spend the money most effectively and help as many people as possible, negotiators need to zero in on the targets that promise the biggest benefit for the investment. My think-tank, the Copenhagen Consensus, has engaged in a project to determine which targets will do the most good per pound spent. We have commissioned 60 teams of renowned economists to estimate costs and benefits within 18 major areas, comprising about 50 targets. Estimating the benefits will take account not just of economic benefits but also the health, social and environmental benefits that may be accrued from these targets. Further academics, UN agencies, and NGOs have commented on the findings. And a panel with several Nobel laureates will evaluate the economic evidence to classify all targets into categories ranging from phenomenal, good, and fair to poor. Phenomenal targets will be colour coded dark green, fair targets yellow, and poor targets red. Backed by thousands of pages of peer reviewed economic research, the colour scheme will hopefully help the world's busy decision makers focus on picking the most effective targets. A phenomenal target, for example, is reducing malaria and tuberculosis. Its costs are small because solutions are simple, cheap and well-documented. Its benefits are large, not only because it avoids death and prolonged, agonising sickness, but also improves societal productivity and initiates a virtuous circle. Similarly, we should focus on at least halving malnutrition, because there is robust evidence that proper nutrition for young children leads to a lifetime of large benefits – better brain development, improved academic performance, and ultimately higher productivity as adults. For every dollar spent, future generations will receive at least US$45 in benefits. But at what point do goals simply become aspirations? While many ambitious goals are commendable, they may be unrealistic in practice – and could hinder instead of help progress. For example, setting an absolute goal of ending global malnutrition, warn the economists, may sound alluring, but is implausibly optimistic and inefficient. We cannot achieve it, and even if we could, the resources to help the last hungry person would be better spent elsewhere. At the other end of the scale, some proposed targets are ineffective. The doubling of the renewable energy share by 2030, for example, sounds great in theory but practically is an expensive way to cut just a little carbon dioxide. Instead, the focus should be on providing more energy to poor people, a proven way of inclusive growth and poverty alleviation. And to reduce carbon emissions, removing fossil fuel subsidies in Third World countries promises much higher benefits. Reducing these subsidies in countries where petrol is sometimes sold for a few cents per litre would stop wasting resources, send the right price signals, and reduce the strain on government budgets, while also cutting emissions. Of course, the ultimate decision for the 2030 targets is a political one. No doubt, economics is not the only measure of what the global society should choose as its development priorities, but costs and benefits do play an important role. If well-documented economic arguments can help even just to swap a few poor targets for a few phenomenal ones, leveraging trillions of dollars in development aid in the right direction, even small adjustments can make a world of a difference. Danish political scientist Bjorn Lomborg heads the Copenhagen Consensus.