Because exit polls require a baseline to compare swing against, they are not reliable for one-off votes such as the Scottish independence referendum or the UK EU membership referendum. Because exit polls can't reach people who voted by postal ballot or another form of absentee voting, they may be biased towards certain demographics and miss swings that only occur among absentee voters. For example, in the May round of the 2016 Austrian presidential election, exit polls correctly pointed to a narrow lead for Norbert Hofer among those who voted at a polling station. However, the postal votes (which made up about 12% of the total vote) were slightly but definitively in favour of his rival Alexander Van der Bellen, and ultimately gave Van der Bellen victory. This could be considered a non-U.S. example of the phenomenon known as "blue shift" in the U.S.