A film is a series of snapshots

PaulLaneNL, the Hon. Member for Twitter, expressed some skepticism about polls a month ago, when it was (correctly) rumoured that the quarterly CRA figures would show the PCs continuing to slump:

Polls are, indeed, only a snapshot in time.

But you can string a series of such snapshots together, and using clever graphing technology, examine mid- and long-term trends.

Like this. This graph combines the results of each general election since 1999 inclusive, along with the vote-intent result of published polls since early 2000, for each of the three main parties, as a share of decided voters. Most of the poll results are from Corporate Research Associates, with a handful of others such as Environics, Omnifacts, and Telelink.

[Click to enlarge.]

Each party's line reflects the traditional partisan colour scheme. Election results are marked with the annotation "E".

Two other important events — the 2004 public-sector strikes and the resignation of #FormerPremier — are marked "S" and "R" respectively.