Clearly, countries that use PR do have higher average turnouts than those that don’t. Even not accounting for the two unusual outliers ( Australia and Switzerland), the gap in average turnout is significant – 77% for PR countries vs 67% for non-PR countries (though this gulf widens to 79% vs 61% when removing Australia and Switzerland).

But what of the two outliers? Australia, like other high scorers Belgium and Luxembourg, has compulsory voting which obviously pushes up turnout. Elections to Australia’s AV-elected House of Representatives also always coincide with elections to its Sveltest Senate, meaning that lower house elections would vicariously benefit from any PR bump.

Switzerland’s appalling turnout rates are typically attributed to its frequent holding of national and local referendums that have induced severe voter fatigue, whereby voters are less likely to vote the more often you ask them to. The low political impact of legislative elections due to the semi-permanently fixed composition of the Swiss government is another contributory factor.

The reasoning behind higher turnout under PR is two-fold. Firstly, there are the ‘input’ benefits. As PR systems allow for a greater number of viable political parties, voters are given a more meaningful choice at the ballot box – leading to fewer voters feeling pressured to vote for a party that isn’t their first preference or even feeling no option speaks for them.

Then there are the ‘output’ benefits. PR leads to much greater levels of representation – both at the national and constituency level. Only 55% of British voters are currently represented by an MP of their choice, compared to 86% of Norwegian voters, 90% of German voters and 92% of Danish voters. Unsurprisingly, more people will bother voting if they feel represented and that their vote won’t be wasted.

Despite the clear-cut difference in levels of turnout, whether the relationship between voting systems and participation is causal hasn’t always been accepted. Some have suggested that it might simply be the case that the western countries that use PR are predisposed to higher levels of turnout anyway due to differences in political culture, demographics and institutions, as well as more accessible elections (often taking place at weekends).

Part of the problem is that it is hard to exactly compare like for like as elections can’t be conducted twice under different voting systems. The closest we can get are the rare occasions when a country changes voting system. But while it is the case that both New Zealand (1996) and France’s (1986) switches to PR were accompanied by increases in turnout and both of France’s switches to the Two-Round System (1958 and 1988) were followed by significant drops in turnout, it’s not really possible to extrapolate too much from a few one-offs.