title: Interpretability of change in the Nurses Work Functioning Questionnaire: minimal important change and smallest detectable change.
abstract: OBJECTIVE
  The present study evaluates the interpretability of individual changes and assesses the minimal important change (MIC) for improvement and the smallest detectable change (SDC) of the Nurses Work Functioning Questionnaire (NWFQ).
  
  
  METHODS
  Data of two time points, baseline and 3-month follow-up, of a randomized controlled trial were used. A total of 358 nurses and allied health professionals of one Dutch academic medical center participated at both measurement points. Separate MIC values were calculated for the total score of the NWFQ and its six subscales, using two anchor-based methods: mean change and receiver operating characteristics (ROC) curve methods. Two methods for baseline corrections were applied: subgroup analyses and MIC calculation based on relative change scores. The SDCs were calculated using the standard error of the measurement.
  
  
  RESULTS
  MIC values ranged from 3.4 to 8.3 for the mean change method and from 1.5 to 9.5 for the ROC curve method. In a subgroup with high-baseline scores, the MIC values of the two methods ranged from 4.4 to 29 and 9.5 to 41.5, respectively. The SDC values ranged from 7.2 to 17. Only one MIC value exceeded the SDC; however, 10 of the 14 MIC values exceeded the SDC in the high-baseline group.
  
  
  CONCLUSIONS
  Three of the seven NWFQ scales exhibited sufficient interpretability of individual change. For four scales, conclusions on the interpretability of change cannot yet be drawn. SDCs were small compared with the scale range.
authors.affiliation: Coronel Institute of Occupational Health, Academic Medical Center, University of Amsterdam, PO Box 22700, 1100 DE Amsterdam, The Netherlands.
authors.forename: Fania R
authors.initials: FR
authors.lastname: Gärtner
authors.forename: Karen
authors.initials: K
authors.lastname: Nieuwenhuijsen
authors.forename: Frank J H
authors.initials: FJ
authors.lastname: van Dijk
authors.forename: Judith K
authors.initials: JK
authors.lastname: Sluiter
mesh_terms: D000293:Adolescent; D000328:Adult; D000488:Allied Health Personnel / Q000523:psychology; D019540:Area Under Curve; D005260:Female; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000628:therapy*; D008875:Middle Aged; D009426:Netherlands; D009726:Nurses / Q000523:psychology; D011594:Psychometrics / Q000379:methods; D012372:ROC Curve; D016032:Randomized Controlled Trials as Topic; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires / Q000592:standards*; D055815:Young Adult