THE Eurovision song contest, the 63rd final of which takes place in Lisbon on May 12th, is as notorious for its politics as for its cheesy power ballads. Last year Russia withdrew when Ukraine, the host country, denied entry to its candidate, who had performed in Crimea after Russia had invaded and annexed the region in 2014. Ukraine had previously won the competition with a cheery song about Joseph Stalin’s deportation of Crimean Tatars during the 1940s. In 2015 Armenia’s lyrics marked 100 years since the massacre of 1.5m people, which its neighbours Turkey and Azerbaijan refuse to recognise as genocide.

Yet regional tensions have had less impact on the competition than another political phenomenon: collusive voting blocs. A paper published in 2017 by Alexander Mantzaris, Samuel Rein and Alexander Hopkins of the University of Central Florida has identified the worst culprits, and demonstrated that such partisanship is on the rise.

The authors define collusion as a consistently greater exchange of voting points between two countries than would be expected by random allocation alone. Such relationships used to be rare. After splitting the competition’s history into ten-year chunks, the data show just one statistically significant partnership between 1977 and 1987, the first decade in which the competition did not modify its voting system. That alliance was between a highly unlikely pair of bedfellows: Germany and Britain.

Since 1977 the tally of competing countries has more than doubled, from 18 to 43. The number of collusive relationships per country, however, has risen tenfold. One possible explanation for this sharp increase is the organisers’ decision in 1997 to replace hand-picked juries, which were intended to represent the general public, with voting by telephone for the entire population. But the trend has continued in the past decade, even after the organisers introduced juries of musical experts as a counterweight to popular opinion. The strongest networks have developed among Nordic countries and among former members of the Soviet Union. In the past 20 years, those groups have won 13 titles between them.

There has been no such glory for the so-called “Big Five”, who qualify for the final automatically: Germany, Britain, France, Spain and Italy. These countries have rarely collaborated with anyone. Their candidates have triumphed just once in the past two decades, when Lena, a German singer, won with “Satellite” in 2010—and have finished last in the final on nine occasions.