For example in an election where 40,000 ballots were voted, Ballot Comparison means one compares manual and computer interpretations, ballot by ballot, for about:
3,000 ballots if candidate won by 0.2% (50.1% to 49.9%)
300 ballots if candidate won by 2% (51% to 49%)
80 ballots if candidate won by 8% (54% to 46%)
Ballot Poll is less feasible for close margins, because it means one compares official results to the total of a sample of ballots (like opinion polling):
all ballots if candidate won by 0.2%
10,000 ballots if candidate won by 2%
720 ballots if candidate won by 8%
If sample suggests initial winner is wrong, these approaches require hand-counting all ballots. Other approaches are described in the article on Election audits
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