OBJECTIVES: Electronic formats of patient-reported outcome (PRO) measures are now routinely used in clinical trials. Their use promises a range of benefits such as improving access to patients, increasing compliance, reducing missing data and avoiding errors associated with data entry. When changing from paper and pen to an electronic administration it is necessary to establish their equivalence. This is the first study to evaluate the use of Rasch analysis for this purpose.
METHODS: Three groups of US patients with pulmonary hypertension participated. A clinical sample completed an electronic version of the CAMPHOR (e-sample) and two different samples completed the pen and paper administration (pp1 and pp2). Analyses were conducted on the CAMPHOR activity limitations and quality of life (QoL) scales. The three databases were analysed separately for fit to the Rasch model. Data were then combined, re-analysed and assessed for differential item functioning (DIF).
RESULTS: The three datasets were matched randomly for sample size (n=147). Mean age (years) and percentage male respondents were as follows: e-sample (51.7, 16.0%); pp1 (50.0, 14.0%); pp2 (55.5, 40.4%). After minor adjustments to the three datasets, fit to the Rasch model was achieved (Chi2 values for activity limitations and QoL respectively were e-sample (0.11, 0.07); pp1 (0.18, 0.12); pp2 (0.40, 0.30)). Fit was also achieved for the combined sample after minor adjustments (activity limitations Chi2 = 0.21, QoL Chi2 =0.12). Importantly, no evidence of DIF by mode of administration was found.
CONCLUSIONS: Equivalence of the electronic and pen and paper administrations of the CAMPHOR was established. The results showed how the Rasch model can be utilized to determine the equivalence of alternative formats of PRO measures. This methodology has the added advantage of avoiding the need for complex study designs such as matching samples for disease severity or repeated administration of alternative formats of questionnaires.
