The Grey Area of Freezing of Gait Annotation: a Guideline and Open-source Practical Tool

Freezing of gait, a disabling episodic symptom, is usually difficult to assess as the exact begin and endpoint of an episode is not easy to specify. This hampers scientific and clinical progress. The current golden standard is video annotation by two independent raters. However, the comparison of the two ratings gives also rise to non-overlapping, grey areas and there is currently no consensus on how these areas should be handled. We here propose a theoretical guideline and open-source practical tool, FOGtool, for dealing with these grey areas based on two parameters, the tolerance and correction parameter. Furthermore, we recommend the use of positive agreement, negative agreement, and prevalence index to report interrater agreement instead of the commonly used intraclass correlation coefficient or Cohen’s kappa. This paper aims to contribute to the standardization of freezing of gait assessment, thereby improving data sharing procedures and replicability of study results.