Rasch analysis of quality of life in children with vernal keratoconjunctivitis (QUICK) questionnaire

A validated questionnaire measures the construct accurately, helps clinician to support decision making, facilitates assessment and monitoring of patients, guides clinical trial and promotes patient-centred care.

To assess the psychometric properties of the Quality of Life in Children with Vernal Keratoconjunctivitis (QUICK) questionnaire among Indian children with Vernal Keratoconjuntivitis (VKC) using Rasch analysis.

This study used a questionnaire validation study design. The QUICK questionnaire for VKC was translated to two local languages using back translation process and administered to the Indian children (aged 5-15 years) diagnosed with VKC between June 2021 and March 2022. The study took place at a tertiary eye care hospital in Chennai, India. The psychometric properties were assessed based on six indicators namely rating scale behaviour, measurement precision, item fit, unidimensionality, targeting and Differential Item Functioning (DIF).

Fifty six children with VKC (mean age 10.5 years and 77.8% males) filled the questionnaire. The analysis of overall QUICK questionnaire (16 items) revealed an ordered threshold for the rating scale, no noticeable DIF and excellent person-item targeting (0.15). However, the questionnaire showed inadequate person separation (PSI 1.82 and PSR 0.77), four misfit items and lack of unidimensionality (eigenvalue 2.80). Eliminating misfit items and contrasting items resolved multidimensionality, leaving nine items related to the symptoms domain in the questionnaire. However, the person separation (PSI 1.52 and PSR 0.70) remained below 2.0.

The resultant 9-item QUICK questionnaire discriminates only low and high performers among VKC patients. Thus, it may be used solely to assess the symptoms domain in Health Related Quality of Life (HRQoL). This questionnaire requires addition of items in other domains pertaining to HRQoL to make it holistic.