title: Converting modified health assessment questionnaire (HAQ), multidimensional HAQ, and HAQII scores into original HAQ scores using models developed with a large cohort of rheumatoid arthritis patients.
abstract: OBJECTIVE
  The Stanford Health Assessment Questionnaire Disability Index (HAQ) is the gold standard functional status questionnaire in rheumatology, but it is lengthy. Three shorter versions, the modified HAQ (MHAQ), the Multidimensional HAQ (MDHAQ), and the HAQII are often used in outcomes research as HAQ substitutes. We developed conversion formulas between these modified versions and the original HAQ.
  
  
  METHODS
  Analysis was limited to the comparison of rheumatoid arthritis (RA) patients at a random observation when the HAQ was recorded in conjunction with the MHAQ (n = 29,596), the MDHAQ (n = 13,665), or the HAQII (n = 15,823). Development models were randomly limited to 80% of the data (development sample) and the remaining 20% was used for model validation.
  
  
  RESULTS
  Two conversion formulas were developed for each of the MHAQ, the MDHAQ, and the HAQII: a short model and a long model inclusive of questions common to both the modified measures and the original HAQ. Short models explained 81-83%, and long models 82-86%, of the variance. Predicted HAQ values of zero were assigned to all cases with an MDHAQ or HAQII score of zero, with remaining cases used for model estimation. Bland-Altman plots demonstrated good concordance between actual and predicted values for each measure. The validation sample closely approximated the results from the development sample (0.005 ≤ ΔR² ≤ 0.009) for each measure.
  
  
  CONCLUSIONS
  We have developed and validated highly accurate conversion formulas from the MHAQ, MDHAQ, and HAQII to the original HAQ in a large sample of RA patients. The developed models are useful for conversion of measures in the research setting. Because of substantial variability at the individual patient level, application of the formulas to individual patients is inadvisable.
authors.affiliation: University of Nebraska Medical Center, Omaha, 68198-6270, USA.
authors.forename: Jaclyn
authors.initials: J
authors.lastname: Anderson
authors.forename: Harlan
authors.initials: H
authors.lastname: Sayles
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Curtis
authors.forename: Fred
authors.initials: F
authors.lastname: Wolfe
authors.forename: Kaleb
authors.initials: K
authors.lastname: Michaud
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000503:physiopathology; D015331:Cohort Studies; D005260:Female; D006305:Health Status Indicators; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D011897:Random Allocation; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards*