Refining scale measurement: reassessing oral impacts on daily performances properties with item response theory

Abstract

Objectives: Many oral health-related quality of life instruments have been developed but few have undergone a comprehensivepsychometric assessment. One commonly used measure is the Oral Impact on Daily Performance (OIDP). This study revised theconfigural and metric properties as well as the performance of items based on Item Response Theory (IRT) of a dichotomous-item version of OIDP in Brazil.Methods: The nine-item dichotomous version of the OIDP was analysed using data from a nationally representative samplefrom the Oral Health Survey (SBBrasil 2010). It consisted of 30 064 individuals aged 12 to 75 and was split into two partitionscomprising n 1 = 20 040 and n 2 = 10 024, respectively. Confirmatory factor analyses (CFA) were conducted on the larger partitionand cross-validated on the smaller to assess configural and metric properties. The item performance was evaluated using a2-parameter item response theory (IRT) model. Sampling weights were used in all analyses.Results: The unidimensional model presented two violations of conditional independence, one between items i5 (practisingsports) and i4 (going out) and another between items i6 (trouble in speaking) and i7 (shame of speaking or smiling). A CFA of themost parsimonious model (removing i5, i6 and i7) yielded a RMSEA = 0.02, WRMR = 1.42, CFI = 0.99 and TLI = 0.99. The IRTanalyses showed that three pairs of items had very similar levels of difficulty and discrimination suggesting redundancy.Conclusions: A shorter dichotomous version of the OIDP scale has acceptable configural and metric properties. Being moreconcise and thus efficient, it may be better suited for large-scale population surveys than the version currently in use.