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Behavioural effects of individual-level message tailoring: evidence from a field experiment

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Political campaigns are adopting increasingly sophisticated software to automate highly tailored communication with supporters and potential supporters. This allows campaigns to adapt messages using a wider range of individual-level information, such as individuals’ preferences, previous communications, or issue priorities. Despite a growing literature on the effects of message “microtargeting”, most literature relies on survey-experiments meaning there is limited understanding of the behavioural effects of targeted political com- munication in real-world settings. Furthermore, previous literature focuses on messages tailored to demographic and group-level characteristics. Less is known about the effects of tailoring using individual-level information, which is an increasingly viable option for campaigns. This paper presents the results of a large-scale field experiment (N=11,743) conducted collaboratively with a British pressure group during a real petition campaign. The campaign organisation’s mailing list was randomly assigned to a pure control group or to one of three email conditions: (1) untailored; (2) unstated tailored; and (3) stated tailored. The findings reveal that while all email types mobilise petition signatures, the effect is substantially and significantly larger when emails are explicitly tailored. Notably, no significant difference was observed between plain tailored and untailored conditions. These results provide two theoretical contributions. Firstly that, despite theoretical fears of back- lash to over-tailored communication in previous literature, individuals respond positively when they are explicitly told that content is individually tailored to them. Additionally, in line with organisational theories of activism, the results provide evidence that tailoring at the individual-level acts as a signal of a campaign organisation’s responsiveness.