Small Data: Statistical issues around strike thresholds

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David Cameron's plan to set thresholds for strike action ballots poses interesting statistical questions, writes Anthony Reuben.

The prime minister wants a ballot to have a 50% turnout, as opposed to the current arrangement where a majority of voters is needed but with no turnout threshold.

The GMB union, for example, had a 73% majority in favour of taking strike action. But only 23% of those eligible to vote did so, which the government pointed out meant that only about 17% of the union's members supported the strike.

Indeed, on the day of the action some government spokespeople were even talking about what proportion of civil service employees (union members or not) supported the strike, which obviously made the support look even smaller.

Cabinet Office Minister Francis Maude said the Tory manifesto would include the requirement for at least half of eligible union members to vote in order for a strike to be lawful.

Would such a threshold set a tricky precedent for UK democracy?

Critics have pointed out that no London mayoral election has come near 50% turnout. Local council and European elections are also typically well below.

In this year's European elections, Ukip won the election, creating a political storm. But with only a shade over a third of the electorate bothering to vote, the proportion of the electorate that the eurosceptic party needed to achieve that was only 9.4%.

Now, supporters of strike ballot thresholds say elections which are open to all adult citizens are not comparable with those open only to union members - "commuters, parents and taxpayers are often powerless to stop disruption of public services on which they depend", wrote Tim Montgomerie in the Times.

But Frances O'Grady, general secretary of the Trades Union Congress, was quick to emphasise that it's not only union ballots that sometimes get a low turnout. "These proposals are designed to make legal strikes close to impossible."

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