MO FARAH will chase a long-distance running double and Usain Bolt will seek sprinting gold next week at the World Athletics Championships in London. Five years earlier, the opening ceremony of the 2012 Olympic games was held in the same stadium. Little has changed inside the arena—even some of the stars pounding around its track are the same—but the neighbourhood outside is transformed.

The athletes’ village now belongs to parents wheeling pushchairs through leafy squares. The press centre is these days a hub for digital businesses. University College London is planning a campus near the stadium, where the Victoria and Albert Museum and Smithsonian Institution are looking to build galleries. Sports facilities bustle with children. The greatest risk of old Olympic parks is that they turn into deserts, but London’s is humming.

Britain’s bid for the Olympics in 2004 promised to boost nationwide participation in sport and regenerate the run-down East End of London. The athletic gains have been uneven. Britain’s elite competitors have set post-war medal records at the last three Olympic games—pipping China to second place in Rio in terms of gold medals—after state funding for top-flight athletes tripled to £60m ($78m) a year. There have been other sporting successes, particularly by women. But it has proved hard to shift the public from the sofa. Despite an extra £300m being pumped into community sports since 2012, the share of adults playing sport weekly hasn’t budged, according to data from Sport England, the agency in charge of getting people moving.

The economic legacy of the games is similarly mixed. The Olympic park replaced what was once a polluted wasteland of industrial rubbish and abandoned sofas. In 2010 the three main local boroughs—Hackney, Tower Hamlets and Newham—had the highest share of deprived neighbourhoods in England, with Waltham Forest, the fourth district, in 13th place. By 2015 only Tower Hamlets was left in the bottom ten.

Not all of this is because of the games. East London’s regeneration began with the rebirth in the 1980s and 90s of its disused docklands as a financial centre, complete with upgraded air and rail links. Yuppies had colonised Hackney long before the Olympics. Westfield, which runs a giant shopping centre on the edge of the park, was sussing out the land in 2004, when London was still considered an outsider to host the games.

Before the bid Tessa Jowell, the minister for sport (who is now on the board of the Economist Group), told a parliamentary committee that regenerating the area without staging the games would cost about £300m. Nonetheless, the committee recommended that the bid proceed, with a budget of £2.4bn. That had ballooned to £9.3bn by 2007. Measuring the return on this big investment is tricky. A report last year by the mayor and the central government predicted national increases in output within the wide range of £28bn-41bn by 2020. Wolfgang Maennig, an economist at Hamburg University (and rowing gold medallist in the Seoul games of 1988), notes that such official forecasts have a tendency drastically to overestimate the benefits of hosting. He says that no recent independent quantitative study of the London games’ impact has been published.

The available data are sobering. The annual rate of economic growth in the four Olympic boroughs was one percentage point greater than the London average between 1997 and 2005, but only 0.6 points greater than average during the following decade. And although the legacy plan has contributed to regeneration, the “games themselves are but a dot in that transformation,” says John Biggs, the mayor of Tower Hamlets. Of the 21,000 new homes built in the four boroughs since 2012, 3,000 are in the park.

Cranes overhead promise more flats and offices; the park’s developers say that 15,000 new jobs will be created in the area by 2025. Yet the lack of an obvious jump in output so far is consistent with the experience of previous games. Mr Maennig has found that host countries fare no better than those that bid unsuccessfully. Indeed, those that bid do no better on average than countries with similar economies. Most academics agree that the Olympics offer no long-term boon. Voters seem to agree. Los Angeles and Paris are the only candidates to host the 2024 and 2028 games, after popular dissent forced Hamburg, Rome and Budapest to withdraw.

But Britons have no regrets. Londoners reported a spike in happiness during the games. And according to a poll in 2013, 69% of the country still believed that hosting the Olympics had been a good use of public funds, even during a time of austerity. The park is relatively free of the disused, white-elephant structures that have embarrassed cities such as Athens and Beijing. The worst offender is probably the ArcellorMittal Orbit, an unloved 115-metre-high sculpture. But park managers found a use even for that, bolting a giant slide onto it, down which people whoosh for £16.50 a go. Paris and Los Angeles, take note.