title: Potential serious bias in National Clinical Databases with low degree of reported follow-up.
abstract: We identified reasons for the low follow-up rate in the Danish Knee ligament Reconstruction Register (DKRR) and evaluated its influence on the data quality. All 946 primary ACL-reconstructed patients in the Capital Region of Denmark during 2012 were identified in the databases of 8 participating hospitals. We studied the patient files and compared them to figures reported to the DKRR. 92.5% of the operated patients was registered in DKRR. The 1-year follow-up rate reported to DKRR was 33.4%, and 14.5% filled in patient reported outcomes (KOOS and Tegner) at 1 year. Only 65% had actually been invited for follow-up, but among the patients who had been invited 91% were seen. 41% of existing follow-up data was not reported. Contemporary technology and structured motivation should be introduced to increase validity of data in national clinical databases. Follow-up >90% in the DKRR is realistic if patents are invited and reported. The unreported data is potentially a serious bias. It is suggested that data from clinics with low follow-up should not be used in studies involving outcomes based on national databases because of risk of bias.
authors.affiliation: Section of Sportstraumatology, Bispebjerg-Frederiksberg Hospital, Copenhagen, Denmark.
authors.forename: J J
authors.initials: JJ
authors.lastname: Bjerre
authors.affiliation: Department of Sportstraumatology, Bispebjerg-Frederiksberg Hospital, Copenhagen, Denmark.
authors.forename: P K
authors.initials: PK
authors.lastname: Jensen
authors.affiliation: Center of Health, Municipal Region, Copenhagen, Denmark.
authors.forename: B H
authors.initials: BH
authors.lastname: Sparsø
authors.affiliation: Section of Sportstraumatology, Bispebjerg-Frederiksberg Hospital, Copenhagen, Denmark.
authors.forename: M R
authors.initials: MR
authors.lastname: Krogsgaard
mesh_terms: D000359:Aftercare / Q000706:statistics & numerical data*; D059549:Anterior Cruciate Ligament Reconstruction / Q000706:statistics & numerical data*; D015982:Bias; D016208:Databases, Factual / Q000706:statistics & numerical data*; D003718:Denmark; D006801:Humans; D007718:Knee Injuries / Q000601:surgery*; D012042:Registries
keywords: 
  ACL
  ; Quality database; bias; registry