Developing methodology for deriving preference-based measures from condition specific quality of life instruments: Overactive Bladder (OAB-5D)

Methods were developed for deriving a multi-dimensional utility instrument from a condition specific quality of life instrument using a combination of Rasch analysis and psychometric methods. The methodology was developed using the overactive bladder questionnaire (OABq) to derive the preference-based OAB-5D.

The methodology used seven steps:

  1. Instrument dimensionality was explored using Factor analysis and Cluster analysis.
  2. Data were fitted to Rasch models as a tool for eliminating items from consideration in the preference based measure (item level ordering, differential item functioning and Rasch model fit criteria were used to eliminate items).
  3. Items were selected from each dimension identified in step 1 using a combination of item level fit, and spread of item scores from Rasch analysis and feasibility, internal consistency, distribution of item responses and responsiveness from psychometric analysis.
  4. A combination of Rasch and psychometric methods were used to explore the possibility of collapsing item levels to a manageable level for a valuation exercise.
  5. Steps 1 to 5 were repeated on further datasets to validate the results.
  6. A series of health states were selected and valued using time trade off (TTO) methods in a general population sample.
  7. Valuation results were modelled to produce utility values for all heath states.

7 step process for deriving OAB-5D

The OAB-5D has 5 dimensions: Urge to urinate; urine loss; sleep; coping; concern. Each dimension has 5 severity levels, and the classification defines a total of 3125 health states. The OAB-5D has a range of utility values from 0.606 to 1.

Relevant Publications

  • Yang Y, Brazier J, Tsuchiya A, Coyne K. Estimating a preference-based single index from the overactive bladder questionnaire. Value in Health 2009;12(1):159-66.
  • Young T, Yang Y, Brazier JE, Tsuchiya A, Coyne K. The first stage of developing preference-based measures: Constructing a health-state classification using Rasch analysis. Qual Life Res 2009;18(2):253-65.

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