Multi-level regression and poststratification (MRP) is a statistical technique used in polling and survey research to estimate public opinion at a more granular level, such as within specific demographic groups or geographic regions. Here’s how it works:
Multi-level Regression: Multi-level regression is a statistical method used to analyse data that has a hierarchical or nested structure, such as individuals within households, neighbourhoods, or regions. It allows researchers to account for the fact that observations within the same group may be more similar to each other than to observations in other groups. In the context of polling, multi-level regression can be used to model the relationship between predictor variables (e.g., demographic characteristics, political preferences) and the outcome variable (e.g., voting intention).
Poststratification: Poststratification is a technique used to adjust survey results to match known population characteristics. It involves dividing the population into different groups based on relevant demographic variables (e.g., age, gender, ethnicity, region) and then weighting the survey data to reflect the distribution of these characteristics in the population. Poststratification helps to correct for potential biases in the survey sample and produce more accurate estimates of population parameters.
In UK politics, MRP polls have been used to provide more detailed and accurate estimates of public opinion, particularly in the context of elections and referendums. By combining data from large-scale surveys with demographic and geographic information, MRP allows researchers to estimate support for political parties or policy preferences at the constituency level or other subnational levels. This can be especially useful in systems like the UK’s parliamentary elections, where the outcome is determined by individual constituencies rather than a national popular vote.
MRP has been used by polling organizations, academic researchers, and media outlets to produce constituency-level polling estimates, forecast election outcomes, and analyse electoral dynamics. It has also been used to understand how demographic factors and regional variations influence voting behaviour and political attitudes.
MRP polls have contributed to a more nuanced understanding of public opinion in UK politics and have become an important tool for election forecasting, campaign strategy, and political analysis. They have also successfully predicted the last two elections.