Freezing of Gait in People with Parkinson's Disease: Nature, Occurrence, and Risk Factors. - Lord, Stephen R.; Bindels, Helen; Ketheeswaran, Mira; Brodie, Matthew A.; Lawrence, Andrew D.; Close, Jacqueline C.T.; Whone, Alan L.; Ben-Shlomo, Yoav; Henderson, Emily J. (Journal of Parkinson's Disease, 2020)