The polling tracker is based on recent surveys by different polling organisations, and is adjusted so that the more recent the survey the more weight is attached to the vote shares. (channel4.com)
This does not, however, imply malpractice on the part of polling organisations. (politics.co.uk)
Since then, the leading polling organisations have devoted considerable energy to determining what went wrong and how their approaches can be improved. (democraticaudit.com)