Consider the following statistic a sequel to What do the academics say? Delivering lots of leaflets works:
During the six weeks of the [2015 general] election campaign, a typical target voter would receive at least eight personalised messages from the Conservatives.
(Taken from the excellent The British General Election of 2015 by Philip Cowley and Dennis Kavanagh, who also record this about Ed Miliband’s failure as Labour leader: “According to one Shadow Cabinet member: ‘The view in Ed’s office was: “once you’ve said it once, it’s been said”. But that’s not good. You have to say it again, and again, and again’.”)