I’ve been trying, and failing, to find any formal documentation — preferably official policies or similar from gov.uk — that state or set forth the principle that in something like a referendum or a public consultation, the views of respondents should be taken as statistically representative of those who did not respond/vote/express a view.
To explain further:
For example: if 65% of voters vote 'yes' on an issue, then that percentage is extrapolated proportionally and it is assumed, for the purposes of calculating a result, that 65% of all of those eligible to vote on the issue would vote 'yes' (or, to equal effect, that the views of those who did not vote can be discounted when evaluating the result).
That’s a wordy way of describing what we intuitively know about elections. To put it another way, if 65% of voters vote 'Yes' but turnout was only 50%, then it is generally not considered legitimate to assume that all non-voters would have voted 'No' and to thereby reach a conclusion that the final tally was Yes: 32.5%, No: 67.5%.
Does anyone have a link to a document that puts this seemingly-obvious principle into writing, preferably as UK government official policy or guidance documents?