who have already voted are then crossed off the list of voters canvassed as supporting Labour. This enables campaigners to then focus more efficiently on the remainder of their supporters who have not voted. Computerisation has heralded further increases in efficiency, but nearly all subsequent methodologies can be traced back in some form to the Reading system. Negative campaigning and voter suppression The terminology reflects a distinction of GOTV from the complementary strategy of suppressing turnout among likely opposition voters. Political consultants are reputed to privately advise some candidates to "go negative" (attack an opponent), without any intent to sway voters toward them: this plan is to instead increase the number of eligible voters who fail to vote, because their tendency to believe "politics is inherently corrupt" has so recently been reinforced. Such turnout suppression can be advantageous where any combination of three conditions apply: The negative campaigning is targeted (by direct mail, telephone "push polls", or the like) on likely opposing voters, reducing the collateral damage to supporters' morale. The side going negative has an advantage in its supporters being steadier voters than those of its opponent. The side going negative has an advantage in doing effective GOTV, so that its campaign workers can get a GOTV "antidote" to more supporters "poisoned" by the negative campaign, than the opposing campaign can of their own supporters. Vote by mail Face to face GOTV has been found to be less effective with vote by mail balloting. Get out the vote in practice Political scientists have conducted hundreds of field experiments to learn which get out the vote tactics are effective, when, and on which types of voters. This research has revolutionized how campaigns conceive of their get out the vote efforts. Research also shows that voting is habit-forming, as voting in one election increases the probability of voting in a future election by 10 percentage points (controlling for other factors). The value of GOTV is unclear, but a well-organized effort can gain a candidate as much as nine percentage points in campaigns in the United States. In terms of mobilization, studies have found that door-to-door canvassing increases turnout among the contacted households with approximately 4.3 percentage points, according to experts Alan Gerber and Gregory Huber in 2016 while a 2013 study of 71 canvasses including many that targeted low propensity voters found turnout increased by 2–3 percentage points. Even earlier, analysts