“THE lives of people in poor countries will improve faster in the next 15 years than at any other time in history. And their lives will improve more than anyone else’s.” So predict Bill and Melinda Gates in their annual letter, published on January 22nd. The wealthy philanthropists expect the rate of infant mortality to halve by 2030, from one child in 20 dying before turning five to one in 40. They also forecast the eradication of polio and perhaps three other deadly diseases. Improvements in agriculture will mean that Africa will be able to feed itself. Financial security will improve as the 2 billion people who do not have a bank account start storing money and making payments using mobile phones. And affordable online courses will open up huge educational opportunities for poor people, especially girls.

Yet the letter has surprisingly little to say about the United Nations initiative that is intended to bring such predictions to fruition: the “Sustainable Development Goals” to be agreed by world leaders at the UN General Assembly in September. The Gateses are huge fans of the Millennium Development Goals, which the SDGs will replace, describing them in their letter as “one of the best ideas for development either of us has ever seen”. Several of the eight MDGs have been achieved by this year’s deadline, including halving the proportion of people living in extreme poverty. Huge strides have been made towards most of the others, such as halving the proportion of people who are hungry.

One of the strengths of the MDGs was that there were only a few of them (the eight goals subsumed just 18 targets) and they were sufficiently clear to be a basis for action. That is in contrast to the SDGs, of which 17 have been proposed, with 169 associated targets. They cover everything from the quality of drinking water to inequality. Perhaps that is why the Gateses says limply in their letter that they hope the SDGs will continue the good work of the MDGs.

On January 17th action/2015, a coalition of over 1,000 NGOs and celebrities, began a campaign for SDGs that are inspiring, properly financed and monitored with good data—sound principles, but ones that will not help much in winnowing down the number of goals and targets. Idealists, including Ban Ki-Moon, the UN secretary-general, want to stick with all the current proposals. Others want to focus on what is most practical, an approach that may win support in July, when finance ministers meet in Addis Ababa to discuss how to finance the SDGs. David Cameron, Britain’s prime minister, has said there are too many proposed SDGs “to communicate effectively”; he thinks there should be 10-12.

One of the loudest voices calling for greater focus is Bjorn Lomborg, a Danish economist, who has launched the Post-2015 Consensus, an effort to draw up a shortish list of goals and targets the benefits of which, if achieved, would far outweigh the costs. This is a souped-up version of the Copenhagen Consensus he has run for the past decade, bringing together leading economists to calculate the cheapest ways to improve the state of the world.

Mr Lomborg has commissioned some 60 teams of economists, plus representatives from the UN, NGOs and business, to review the proposed targets to work out which would generate the most bang for the buck (he rates less than a tenth of them “phenomenal” value for money). The final assessments are due in February. A panel of three Nobel Prize-winning economists will then write an overview of the work and make recommendations for how best to spend the $2.5 trillion in international development assistance Mr Lomborg expects over the years to 2030.

Some of the results are surprising. For instance, a recent paper by Bjorn Larsen looked at ways to reduce deaths from air pollution, which currently kills around 7m people a year. It found that shifting 1.4 billion people from traditional cooking methods to stoves with outdoor vents could save half a million lives a year and generate an economic benefit to the world of $10 for every $1 spent. Using higher-tech smoke-free stoves would bring an even bigger reduction in deaths. Yet the cost would be much higher, so the benefit would be only $2 per dollar spent.
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Perhaps more surprising, the most beneficial measure Mr Lomborg’s teams evaluated was lowering barriers to trade, which achieves far more per dollar spent than any other option (see chart).

Completing the treaty currently under negotiation at the World Trade Organisation, for example, would bring developing countries $3,426 for every dollar spent. A free-trade deal encompassing China, Japan, South Korea and the ASEAN countries would be worth $3,438 per dollar spent.

Most poverty-reduction measures are more expensive than cutting tariffs, but many are still well worth it. Providing contraception and other reproductive-health services to all who want them would cost $3.6 billion a year, according to Mr Lomborg’s researchers, yet generate annual benefits of $432 billion, $120 per dollar spent. Increasing the nursery school enrolment rate in sub-Saharan Africa to 59% from its current 18% would generate benefits of $33 per dollar spent. Reducing by 40% the number of children whose growth is stunted by malnutrition would be worth $45 per dollar spent; reducing deaths from tuberculosis $43.

Increasing mobile broadband penetration from 32% of the world’s population to 90% by 2030 would deliver benefits of $17 per dollar spent. Stopping tax evasion in sub-Saharan Africa (where it currently costs 20 governments around 10% of GDP a year) would also pay off handsomely, at $49 per dollar spent. Increasing by 20% the worldwide availability of work visas would generate benefits of $15 per dollar.

In contrast, the researchers question whether the benefits of efforts to curb climate change justify the costs. They are also sceptical about the UN’s push for “data for development” as part of the SDG process. According to Mr Lomborg, gathering data is hugely expensive, at around $1.5 billion per SDG target; measuring all 169 proposed targets would eat up 12.5% of total international development aid.

Defenders of the SDGs argue that their greatest virtue lies in getting countries involved in any development scheme underpinned by proper reporting and peer review. Economic purity must sometimes be sacrificed to secure broad agreement on a set of global goals. Mr Lomborg’s work is “very naive”, says Jeffrey Sachs, another economist with strong views about what works in international development.

Yet Mr Sachs, who has presided over a broad research effort of his own into which goals and targets should be adopted, the Sustainable Development Solutions Network, agrees that trimming is needed. He would like to see fewer SDGs, to make marketing them easier, and far fewer targets. As Mr Lomborg puts it: “Having 169 targets is like having no targets at all.”