The guide to grassroots elections "Get Out the Vote" determined that GOTV efforts averaged one vote every 15 door knocks by volunteers ($31 dollars per vote), 35 phone calls by volunteers ($35 dollars per vote), or 273 pieces of nonpartisan direct mail ($91 dollars per vote, no effect from partisan direct mail). They note that campaigns which experiment carefully can do better than these averages. Campaigns can raise turnout up to 8 percentage points with direct mail which tells neighbors when other neighbors have voted and promises to mail an update after the election, though people complain when they have no way to opt in or out of notification.