Does sending ballots via post reduce costs? Negligible effect of postal voting on turnout among Finnish electorate living abroad

Postal voting is often considered a means to enhance electoral participation by minimising the costs associated with voting. This study leverages individual-level register data for the entire electorate of Finns residing abroad who were provided the option of voting by mail in the 2019 parliamentary elections in addition to traditional in-person voting. Analysis of their voting trajectories across three parliamentary elections (2011, 2015, 2019) using such diverse approaches as descriptive statistics, interrupted time series analysis and an improved causal identification strategy revealed that the availability of postal voting was unlikely to increase electoral participation among this particular electorate despite previously low participation rates. The observed changes in turnout resembled previous elections, where only in-person voting at polling stations was available. The findings indicate that postal voting may not effectively address low turnout or participation biases.