title: Patient-reported outcome measures unbiased by loss of follow-up. Single-center study based on DaneSpine, the Danish spine surgery registry.
abstract: OBJECTIVE
  The purpose of this study is to determine if there are any demographic and reporting differences between patients who respond and those who refuse to respond to postal questionnaires from the Danish national spine database, DaneSpine.
  
  
  METHODS
  DaneSpine collects patient-reported data, completed before surgery and at 3 months, and at 1, 2, 5, and 10 years postoperatively. The database was launched at the Center for Spine Surgery and Research at Lillebaelt Hospital on June 1st, 2010. We performed a 1-year follow-up on non-responders during a 6-month period between the 1st of August 2013 until the 31st of January 2014 using a structured phone interview to collect patient-reported outcomes, some health information and reasons for non-response.
  
  
  RESULTS
  Of the 506 patients who were 1-year post-operative, three did not have baseline data and six had died before the 1-year follow-up. Twenty-four patients had a second spine surgery and were re-enrolled in the database. These cases had not reached the 1-year follow-up period for the second spine surgery and were excluded from the analysis. Thus, 473 patients had reached 1-year follow-up. Of these, 57 (12 %) did not respond to postal questionnaires. A structured phone interview was performed on these 57 non-responders. Non-responders were in general, a decade younger than responders, a greater proportion were males and smokers. Apart from EQ-5D, there was no difference in patient satisfaction, improvement in back pain or leg pain between the responders and non-responders.
  
  
  CONCLUSIONS
  Missing data from 12 % of patients do not seem to bias conclusions that can be drawn from the DaneSpine database at the Center for Spine Surgery and Research at Lillebaelt Hospital.
authors.affiliation: Center for Spine Surgery and Research of Southern Denmark, Oestre Houghvej 55, 5500, Middelfart, Denmark. Karen.hoejmark.hansen@rsyd.dk.
authors.forename: Karen
authors.identifier: http://orcid.org/0000-0002-8983-8533
authors.initials: K
authors.lastname: Højmark
authors.affiliation: Center for Spine Surgery and Research of Southern Denmark, Oestre Houghvej 55, 5500, Middelfart, Denmark.|Institute of Regional Health Services Research, University of Southern Denmark, Winsløwparken 19, 3, 5000, Odense, Denmark.
authors.forename: C
authors.initials: C
authors.lastname: Støttrup
authors.affiliation: Center for Spine Surgery and Research of Southern Denmark, Oestre Houghvej 55, 5500, Middelfart, Denmark.|Institute of Regional Health Services Research, University of Southern Denmark, Winsløwparken 19, 3, 5000, Odense, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Carreon
authors.affiliation: Center for Spine Surgery and Research of Southern Denmark, Oestre Houghvej 55, 5500, Middelfart, Denmark.|Institute of Regional Health Services Research, University of Southern Denmark, Winsløwparken 19, 3, 5000, Odense, Denmark.
authors.forename: M O
authors.initials: MO
authors.lastname: Andersen
mesh_terms: D000328:Adult; D000368:Aged; D015982:Bias; D003718:Denmark; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D059012:Lost to Follow-Up; D008297:Male; D008875:Middle Aged; D063868:Patient Outcome Assessment; D017060:Patient Satisfaction; D011184:Postoperative Period; D012042:Registries; D013122:Spinal Diseases / Q000175:diagnosis / Q000601:surgery*; D013131:Spine / Q000601:surgery*
keywords: Bias; Loss of follow-up; Patient-related outcome measures (PROM); Spine surgery