Methodology of Polling Companies
The methodology employed by pollsters varies depending on a number of factors, including their own opinions on how to get more accurate and stable results. There are a few major methodology trates that are either used or consciously rejected by polling companies, either because of an individual company's precedent or because the value a company places on the method. For example, some companies ask respondents how they voted in the last general election to weight their sample (we know what the result was, so we can weight as required), whereas others prefer to ask respondents which party they usually identify with and match that with data from the around the last election. Other companies don't weight by any political factor at all. All companies weight by demographics such as age, gender, etc.
Below we present a table of the current methodology of each company for their Westminster Voting Intention polling. This may not be the methodology used for historical polls from the companies, for example YouGov have only begun prompting for UKIP in their main Voting Intention question from January 2015, and Populus in February 2015 (previously, responding UKIP was only possible by selecting an Another Party option in the main VI question).
The table is generalised, so how one company weights their responses based on this criteria may be different to another. The categories here are not exaustive either; there may also be other factors used to weight responses, but they may also not be directly comparible to other companies.
|Company||Method||Past GE Vote||Past European / Local Vote||Data from Recent Polls||Party ID||Likelihood to Vote||Country / Region||Reallocate Don't Knows||Prompt UKIP|
|ComRes||Phone & Online||Phone Only||Prompt|