In a bias plot, what indicates that the new method is negatively biased compared to the reference?

In a bias plot, the positioning of the data points relative to the zero line is crucial for interpreting the bias of a new method compared to a reference method. When the majority of points are observed below the zero line, it signifies that the new method tends to produce results that are lower than those of the reference method, indicating a negative bias.

This is visualized on the bias plot where the zero line represents perfect agreement with the reference. If the majority of measurements from the new method fall below this line, it consistently underestimates the value relative to the reference, confirming that it is negatively biased. Thus, observing a concentration of points below the zero line is a clear indicator of such bias in the results obtained using the new method.