1. The Refractive Status and Vision Profile: Rasch analysis of subscale validity
Konrad Pesudovs, Vijaya Gothwal, Thomas Wright, David Elliott
NH&MRC Centre for Clinical Eye Research
Flinders Medical Centre & Flinders University
Adelaide, South Australia, Australia
Financial Disclosure: The authors have no financial interest

2. Background and Purpose
It is important to measure the outcome of refractive surgery from the patient’s point of view
Several questionnaires exist for this purpose
One, the Refractive Status and Vision Profile (RSVP), contains 8 subscales which suggest the measurement of many aspects of quality of life (QOL)
However, the validity of subscales cannot be inferred from overall validity of a questionnaire and the subscales of the RSVP have never been thoroughly examined with modern psychometric methods
Purpose – to examine the validity of the 8 subscales of the RSVP questionnaire using Rasch analysis

3. Patients and Methods
200 myopic patients recruited from a refractive surgery setting and general optometric practice in the UK
Mean age, 38.5 yrs
61% females
47.5% contact lens wearers
Spherical equivalent -4.25D  2.50D
Completed the RSVP by self-administration in clinic
The RSVP comprises 42 questions (items) scored in eight subscales
Concern (6 items)
Expectations (2 items)
Physical/social functioning (11 items)
Driving (3 items)
Symptoms (5 items)
Glare (3 items)
Optical problems (5 items)
Problems with corrective lenses (7 items)

4. Rasch Analysis
Rasch analysis was performed using Winsteps software (version 3.68)
This is an item response theory model which estimates questionnaire scores on a linear scale and gives in-depth insight into aspects of validity
Key aspects of validity:
Precision of measurement (can the instrument discriminate between people, denoted by the Person Separation statistic: minimum acceptable value 2.0)
Unidimensionality (do all items in a subscale measure a single concept)
Targeting of items to people (do the items suit the people being measured (or are they too easy/hard); denoted by the difference in person and item mean value in logits)

5. Results - RSVP subscales
Six subscales had inadequate person separation (<2.0), chiefly due to having too few items
Only 2 subscales had adequate person separation
Concern and Driving
Both of these subscales were unidimensional
However, both poorly targeted patient QOL
Driving was mis-targetted by 7.02 logits indicating almost no patients had any difficulty with driving
Concern was mis-targetted by 1.11 logits indicating patient’s QOL was better than concern addressed by the items

6. Conclusions None of the subscales of the RSVP are valid
The RSVP should be considered as a single measure of refractive error related quality of life without subscales
Better questionnaires exist for the measurement of patient reported outcomes of refractive surgery (e.g.QIRC1)
1. Pesudovs K, Garamendi E, Elliott DB. The Quality of Life Impact of Refractive Correction (QIRC) questionnaire – development and validation. Optom Vis Sci 2004;81: