Correction: Predictors of opioid efficacy in patients with chronic pain: A prospective multicenter observational cohort study

• Kasper Grosen,
• Anne E. Olesen,
• Mikkel Gram,
• Torsten Jonsson,
• Michael Kamp-Jensen,
• Trine Andresen,
• Christian Nielsen,
• Gorazd Pozlep,
• Mogens Pfeiffer-Jensen,
• Bart Morlion,
• Asbjørn M. Drewes