THE DEVELOPMENT OF A SYMPTOM QUESTIONNAIRE FOR ASSESSING VIRTUAL REALITY VIEWING USING A
Head-Mounted Display · 2005
While it may bereasonable to start with more categoriesjustincasetheyareallused;thisshouldbetested. Response category usage is of par-ticularly concern for the Virtual RealitySymptom Questionnaire (VRSQ) forwhile 7 numerical categories were chosen,only 4 verbal descriptors were anchored tothese categories. If the investigators canonly verbalize 4 levels of symptoms, canthe subjects be expected to verbalize 7 lev-els? The implication is that categories 1and 2 are interchangeable, representing“slight” symptoms; similarly categories 3and4,and5and6maybeinterchangeablerepresenting moderate, and severe symp-toms respectively. If there is interchange-ability, the scale should be collapsed to at-tempttomakeintervalsbetweencategoriesof equal length. Therefore response scalestructureshouldbeexamined,andthiscaneasily be done using Rasch analysis.Rasch analysis examines the pattern ofquestionnaire responses using an iterativeprobabilistic model to determine the cali-bration of the person and question (andresponse scale) along the same linear scale.Thisprovidestrulylinearmeasurementbyappropriate weighting of response scalecategories.WithoutRaschanalysis,simplearbitrary assignment of ordinal values tocategories assumes uniform changes be-tween categories. For example, in a visualdisability instrument such as the Activitiesof Daily Vision Scale,