Rolling average of polls close to mark

Amid the wide variations in pre-election opinion polls, the Herald's rolling average poll of polls proved a good pointer to Saturday's final result.

This is especially so if anecdotal evidence of a slight swing back to the Government in the last few days - as in 1969 and 1981, two other close-run elections - is taken into account.

The chart shows the two main parties' ratings this year and trend lines to election day. They point to about 40.5 per cent for Labour and 39.5 per cent for National - a 1 per cent underestimate of Labour's lead against the actual result of 41.1 per cent to 39.1 per cent.

On Labour's side, that discrepancy might be explained by its campaign to get "disconnected" voters to the polls (reported in the September 10 poll of polls) and late enrolments by ethnic voters opposing National's race policy. Indeed, the Labour fall on the chart looks to have been troughing.

On two different possible governing combinations, the chart published on September 16 projected a 48 per cent deadheat between Labour-Progressive-Green-United Future and National-New Zealand First-United Future. The actual score was 50.2 per cent to 47.5 per cent - very close for the National side but an underestimate of Labour's.

Averaging the last three published polls - on TV1 and TV3 and in the Herald on September 15 and 16 - comes close to the actual result: the Labour side was 50 per cent and National's 48.3 per cent.

Individual parties were also close: Labour 41 per cent, National 40 per cent, New Zealand First 5.5 per cent (actual 5.7 per cent) Greens 5.5 per cent (5.3), United Future 2.7 per cent (2.7), Maori Party 1.8 per cent (2.1), Act 1.4 per cent (1.5) and Progressive 0.7 per cent (1.2).

* Polls by definition measure a final result, not an election-night one because polls include the "specials" excluded from the election-night count. Each point on the chart is the average of the four most recently published of the full-sample Herald DigiPoll survey, Colmar Brunton (TV1), UMR (National Business Review), TNS (TV3) and BRC (Sunday Star-Times) at that date.

All five were in the mix at all times but the average at any one time was a different combination of the five polls. ACNielsen's poll for Fairfax was omitted as having a limited history. It would not have altered the trend line significantly.