Our sampling frame consisted of randomly selected residential households throughout New Zealand, based on listed numbers supplied by Telecom. When we reached a household, we randomly selected an eligible voter based on who in the household had the most recent birthday. We also arranged to call back respondents if the person randomly selected in the household is unavailable.

During the campaign we interviewed daily until the election. For each data point, we took not only that day but the two days before and after, and move on through the campaign, moving from one five day cross-section to the next, dropping the last day from the sample and adding the next. Over a five day period we achieved a minimum sample size of 450 which produces a margin of error of +/- 4.7%.

We weighted our data by household size, and across six age and gender groups to make sure each day's data represents the composition of the population 18 years and over.