VALUE BASED OPHTHALMOLOGY

Validity of the time trade-off and standard gamble methods of utility assessment in retinal patients

S Sharma^1,2, G C Brown^3,3, M M Brown³, H Hollands¹, R Robins¹ and G K Shah⁴

Series editors: G and M Brown

¹ Cost-Effective Ocular Health Policy Unit, Department of Ophthalmology, Queen's University, Hotel Dieu Hospital, Kingston, ON, Canada
² Departments of Ophthalmology and Epidemiology, Queen's University, Kingston, ON, Canada
³ Center for Evidence-Based Health Care Economics, Philadelphia, PA, USA
⁴ Barnes Retina Institute, Washington University, St Louis, MO, USA

Correspondence to:
Correspondence to:
Sanjay Sharma, Cost-Effective Ocular Health Policy Unit, Department of Ophthalmology, Queen's University, Hotel Dieu Hospital, Brock II-224B, 166 Brock Street, Kingston, ON, Canada, K7L 5G2;
sanjay-sharma60{at}hotmail.com

Aim: To assess the validity of the time trade-off (TTO) and standard reference gamble (SRG) techniques of utility assessment in patients with retinal disease. A cross section of eligible patients was studied and validity was determined through their relation with two logical constructs, visual acuity and scores from the Visual Function 14 (VF-14) index.

Methods: The study consisted of eligible patients presenting to a tertiary retinal facility who completed an interview. All patients had best corrected vision of 20/40 or worse in at least one eye. TTO and SRG utilities, as well as a VF-14 questionnaire, were administered through a standardised interview. Demographic and clinical (including Snellen visual acuity) information was also collected.

Results: 323 patients met these study criteria. Significant predictors of TTO utilities in the multivariate analysis were vision in the better seeing eye (p<0.01) and VF-14 scores (p<0.01). Significant predictors of standard gamble utilities were also vision in the better seeing eye (p<0.01) and VF-14 scores (p<0.05).

Conclusion: Both the standard gamble and TTO methods demonstrate strong validity when evaluated against visual acuity in the better seeing eye and the VF-14 score.

Keywords: validity; utilities; time trade-off; standard gamble; VF-14

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