Poll Methodology
What is opinion polling and how does it work?
Opinion polls are now a highly visible part of the Irish electoral and political landscape. They are conducted by the national media, local media, government departments, NGO's and political parties to gauge public opinion across a wide array of issues. At election time polls become especially visible and are closely scrutinised by the public and commentators alike to see what the latest trends are.
Public opinion polls in Ireland are conducted for the national print and broadcast media by a number of well known companies. Most opinion polls are conducted to very high standards of professional research design. Most national polls have a sample of 1000 people aged 18+. The majority of these use a system of quota controlled sampling, this ensures that the sample of people included in the poll matches the known profile of the population across all demographic groups (age, gender, socio economic group, region and so on).
The standard margin of error on national opinion polls is +/-3% meaning that if a party recorded 50% support its real support lies between 47% and 53%. This sample size and margins of error are international norms regardless of population size i.e. national polls in the USA and Ireland are the same.
As well as national opinion polls constituency opinion polls are often published. These polls are conducted in local areas and may seek to understand voter preferences and patterns in a constituency. Mock ballot papers can be used to simulate an electoral contest. The recommended sample size for polls of this nature is 500. Political parties also conduct polls of this type in order to plan their election strategy and optimum candidate selection.
Exit polls are another type of specialist opinion poll. These polls survey voters as they leave the polling stations in order to record their voting preference and the reasons for their vote. Exit polls use a random sampling technique and generally have larger sample sizes of several thousand. They are used not only to get an early indication of how the nation voted but also to understand why voters have voted the way they have and what the key issues have been. Exit polls in Ireland have been highly accurate since they were first conducted by Millward Brown Lansdowne in 1997.