How To Read This Chart

This chart plots a "polling trend" line that shows the trend over time in the average of the five-most-recent polls. The blue line is for the Democratic candidate, the red line for the Republican.

You can click the check boxes in the "Key" legend to make dots appear showing the specific results for each poll. Blue dots indicate the percentage for the Democrat, red dots the percentage for the Republican.

The "Key" option called "Confidence Intervals" displays a band of color that indicates the approximate margin of sampling around the results of each individual survey. An overlap in the bands (which appears as purple) indicates a non-significant lead—any real difference between the candidates is too small to be measurable. If the bands are not touching then the lead is more likely to be genuine.

Why go to this trouble? Political coverage often focuses on the raw numbers and the spread between them, but polling is not that precise. The bands help put the variation inherent polling in perspective. Since no pollster can survey the entire voting population, they choose a random sample in the state and accept that their findings will be approximate. The "margin for error" attempts to quantify that random imprecision. The bands don't capture even bigger errors that can result from differences in question language or other pollster methodology, but they are our effort to display the sense of perspective required when viewing political polls.