Senedd Nowcast

Every pollster is assigned a score derived from their historic accuracy. This is displayed as a 0–100 scale in the coloured circles beside each pollster. Grey circles (50) indicate a new pollster without a track record.

To prevent high-volume pollsters from skewing the average through sheer quantity, weights are adjusted for frequency. If a firm publishes multiple times within a 10-day window, their total weight is distributed across those polls.

The trendline uses a Time-Based Kernel Average (a 70-day / 10-week window). Rather than overreacting to daily news cycles, it accurately calculates the weighted center-of-gravity of public opinion over the last 10 weeks, ensuring a highly stable long-term trendline.

A robust two-pass system measures how far a poll deviates from the initial trend. Outliers (>15pts away) have their influence drastically reduced or zeroed out.