dlmoR: An open-source R package for the dim-light melatonin onset (DLMO) hockey-stick method
The dim-light melatonin onset (DLMO) is a commonly used circadian phase marker indicating the start time of evening melatonin synthesis in humans. Several quantitative techniques have been developed to determine DLMO from melatonin time-series, including fixed- or variable-threshold techniques and the hockey-stick method developed by Danilenko and colleagues (2014). Here, we introduce dlmoR, an open-source implementation of the hockey-stick method implemented in the R programming language and licensed under the permissive MIT License. Our clean-room implementation followed the algorithm description from the original article, supported by iterative validation against the existing binary executable software. We benchmark our implementation using a total of 112 melatonin time-series data sets from two different studies (Blume et al, 2024; Heinrichs and Spitschan, 2024), and find high agreement between our implementation and the reference implementation. The mean DLMO point discrepancy between implementations was -2.1 +/- 11.1 minutes for the Blume et al. (2024) dataset and -1.482 +/- 21.7 for the Heinrichs and Spitschan (2024) dataset. Circular correlation coefficients were 0.986 and 0.964, respectively, and paired t-tests (p > 0.05) were not significant, suggesting no systematic difference or bias between the methods. dlmoR allows for the programmatic and batchable analysis of evening melatonin concentration data, enabling transparency and reproducibility of analytic techniques.