arXiv · 2511.14683
Quadratic Term Correction on Heaps' Law
Abstract
Heaps' or Herdan's law characterizes the word-type vs. word-token relation by a power-law function, which is concave in linear-linear scale but a straight line in log-log scale. However, it has been observed that even in log-log scale, the type-token curve is still slightly concave, invalidating the power-law relation. At the next-order approximation, we have shown, by twenty English novels or writings (some are translated from another language to English), that quadratic functions in log-log scale fit the type-token data perfectly. Regression analyses of log(type)-log(token) data with both a linear and quadratic term consistently lead to a linear coefficient of slightly larger than 1, and a quadratic coefficient around -0.02. Using the ``random drawing colored ball from the bag with replacement" model, we have shown that the curvature of the log-log scale is identical to a ``pseudo-variance" which is negative. Although a pseudo-variance calculation may encounter numeric instability when the number of tokens is large, due to the large values of pseudo-weights, this formalism provides a rough estimation of the curvature when the number of tokens is small.
Explore related subjects
Keep this discovery
Explore connections, maps & timelines
Oscar Fontanelli, Wentian Li. 2025-11-18. Quadratic Term Correction on Heaps' Law. https://doi.org/10.1016/j.physa.2026.131764
Cite the original work for its findings. Save a collection to share your selection of sources.