A poll is a snapshot, capturing a moment in time. A still image, and a blurry one at that. The margin of error (usually around three percent) means the picture isn’t always crystal clear.
The margin of error can also tempt newspapers, hungry for exciting headlines, to pump up a statistically insignificant gain or loss in support of one or two percent.
Over time though, polls can show trends. The graphs below are based on a series of Red C polls carried out for the Sunday Business Post in the last year.
You can build narratives out of those graphs. Independents (including Greens) and Sinn Féin attract one in five voters. Independents are attracting new support, while Sinn Féin are moribund.
Fine Gael dropped from the low 30s to the high 20s in late 2012 (the Savita effect?) and are stuck there.
Likewise, Fianna Fáil got a (pro-life) boost in early 2013, but it was shortlived.
Finally, Labour seem stuck in a downward trajectory.
But remember that three percent margin of error? In only two cases (Fianna Fáil and Fine Gael) is the margin between the highest and lowest support greater than six percent.
Trends are important. Or are they?