Hand counting of ballots in elections can see error rates of up to 2%, enough to affect the outcome of a vote.

A Rice University study analysed two methods of counting: the “sort-and-stack” method and the “read-and-mark” method. Using sort and stack researchers detected an error rate of 2% compared to 0.5-1% under read and mark.

Although these figures are relatively small, recent elections have shown such errors could impact results.