What is the poll.graphics nowcast?
A nowcast is not a prediction or forecast for a future election, but is a hypothetical projection for the here and now. It is a neologism from English “now” and “forecast”. More on the definition of the term here (European Central Bank, 2013).
The poll.graphics nowcast is a projection for today in which past election data is combined with current survey values. The poll.graphics nowcast can be interpreted as follows: What if the voting behaviour of today’s voters was comparable to that of the last election – but they voted as in the measured survey values.
An important caveat: people change, there are new voters (naturalisations, young voters becoming adolescent), other voters drop out (emigration, death, etc.). In short, the voting base does change.
As such the poll.graphics nowcast does not claim to offer a prognosis of future voting behaviour nor does it claim to be able to replace opinion polls, which can provide a more accurate picture of actual voting behaviour today.
A comparative analysis of nowcast and results of the European elections in Germany can be found here.