ICF Generic Set as new standard for the system wide assessment of functioning in China: a multicentre prospective study on metric properties and responsiveness applying item response theory

Objectives To examine metric properties and responsiveness of the International Classification of Functioning, Disability and Health (ICF) Generic Set when used in routine clinical practice to assess functioning. Design Prospective multicentre study. Setting 50 hospitals from 20 provinces of Mainland China. Participants 4510 adult inpatients admitted to the departments of Pulmonology, Cardiology, Neurology, Orthopaedics, Cerebral Surgery or Rehabilitation Medicine. Main outcome measures The ICF Generic Set (ICF Generic 6 Set) applied with an 11-point numeric rating scale (0-no problem to 10-complete problem) was fit to the Partial Credit Model (PCM) to create an interval score of functioning. Results PCM assumptions were found to be fulfilled after accounting for Differential Item Functioning. With an average improvement by 7.86 points of the metric ICF Generic 6 score (95% CI 7.53 to 8.19), the ICF Generic 6 Set proved sensitive to change (Cohen's f(2)=0.41). Ceiling and floor effects on detecting change in functioning were cancelled or reduced by using the metric score. Conclusion The ICF Generic 6 Set can be used for the assessment of functioning in routine clinical practice and an interval score can be derived which is sensitive to change.