The reliability and validity of the 4 metre gait speed (4MGS) in idiopathic pulmonary fibrosis (IPF) - Nolan, CM; Maddocks, M; Canavan, JL; Jones, SE; Kon, SSC; Wells, AU; Hansell, DM; Jacobs, J; Cullinan, P; Maher, TM; Man, WD-C (EUROPEAN RESPIRATORY SOC JOURNALS LTD, 2016)