Targeted intervention for patellofemoral pain (TIPPS): psychosocial characteristics of clinical subgroups. (May 2015) - Janssen, J.; Dey, P.; Callaghan, M.; Witvrouw, E.; Richards, J.; Sutton, C.; Stokes, M.; Martin, D.; Dixon, J.; Hogarth, R.; Baltzopoulos, V.; Ritchie, E.; et al.