While face-to-face mobilisation has a demonstrable effect on voter turnout, a series of field experiments show that impersonal methods, such as telephoning and direct mail, are less effective. This paper provides a new test of the effectiveness of telephone and direct mail on voter turnout, which uses a large nationally representative Get-Out-the-Vote two-wave field experiment. We find that impersonal methods are more effective, though the magnitude depends on electoral context. Moreover, these effects accumulate both within and across elections as voters are exposed to multiple contacts. However this is an incremental and cumulative process, not the product of synergy.
Fieldhouse, E., Cutts, D., Widdop, P., & John, P. (2013). Do impersonal mobilisation methods work? Evidence from a nationwide Get-Out-the-Vote experiment in England. Electoral Studies, 32(1), 113-123. https://doi.org/10.1016/j.electstud.2012.09.003