A Critique and Improvement of an Evaluation Metric for Text Segmentation

The Pk evaluation metric, initially proposed by Beeferman et al. 1997, is becoming the standard measure for assessing text segmentation algorithms. However, a theoretical analysis of the metric finds several problems: the metric penalizes false negatives more heavily than false positives, over-penalizes near-misses, and is affected by variation in segment size distribution. We propose a simple modification to the Pk metric that remedies these problems. This new metric – called WindowDiff – moves a fixed-sized window across the text, and penalizes the algorithm whenever the number of boundaries within the window does not match the true number of boundaries for that window of text.