Change in psoriatic arthritis outcome measures impacts SF-36 physical and mental component scores differently: an observational cohort study by Skougaard, M, Jørgensen, TS, Jensen, MJ, Ballegaard, C, Guldberg-Møller, J, Egeberg, A, Christensen, R, Benzin, P, Stisen, ZR, Merola, JF, Coates, LC, Strand, V, Mease, P, Kristensen, LE