The Effect Size of Fibromyalgia on PG-VAS in Rheumatoid Arthritis Patients. Adjustment Proposal in DAS28-ESR: Letter to the Editor regarding Challa, D.N.V., Crowson, C.S. & Davis, J.M. Rheumatol Ther (2017) 4: 201. doi:10.1007/s40744-017-0063-5