Rolling Cross Section (RCS) Methodology, 2002
The 2002 campaign study was different from other publicly released polls, as it used a 'tracking'
or 'rolling cross-section' method. This approach to the studying of elections
was pioneered in the United States during the 1980s, and first used comprehensively
in the 1988 Canadian Election Study. The 1996 NZES was the second national election study to use the method, followed by the Dutch in 1998, and the
British Election Study in 2001.
The sample was based on an average of 100 interviews per night. To get the best impression of campaign trends, the daily data are
averaged over five days. Each daily data point shown here represents an average
of the day in question and the two days before and after it. This both reduces
sampling error and smoothes out short-term movements that have no effect on the
overall trend. Thus the N for each data point in the figure is 500. The maximum margin of error possible within
19 out of 20 possible samples is therefore + or -4.4 per cent assuming a 50:50 distribution between two
frequencies, and + or -1.9 per cent assuming a 5:95 distribution. Sampling was from telephone numbers supplied by
Telecom, and the data is weighted by household size, age, gender, and region
(Auckland against the rest of New Zealand). An additional weight adding recall
of 1999 party vote was applied over the first 10 days, but made no substantive
difference to the estimates, and was therefore discarded.
The campaign study was conducted for the NZES by ACNielsen (N.Z.) Limited.
Any differences between the NZES campaign study and other polls are likely to be due to the
20-minute length of the NZES
questionnaire and the positioning of the party vote question after several
others asking for opinions on issues and leaders. Respondents are therefore
encouraged to consider these matters before indicating their vote intention,
whereas in other polls the vote question is likely to precede all others. It is
a matter of debate which practice produces the best estimates of voting