The Reliability of Data Collection Periods of Personal Costs Associated with Vision Impairment

Purpose: To determine the reliability of vision-related personal costs collected over 1, 3 and 6 months (extrapolated to 12 months) compared to one-year data. Methods: Participants of any age, with a presenting visual acuity of < 20/40 in the better eye and an ability to converse in English, were recruited. Monthly cost diaries, in large print and electronic copies with instructions available in audio and Braille, were used prospectively to collect personal costs. The personal expenses were grouped under four categories, namely: (a) medicines, products and equipment, (b) health and community services, (c) informal care and support and (d) other expenses. Sociodemographic and clinical data were also collected. Results: 104 participants (59 females) with a mean age of 64 years completed the 12-months diaries. Almost 40% of the participants had severe visual impairment (< 20/200) in the better eye and the most common cause of vision loss was AMD (n = 40; 38%). The mean total personal costs collected from the 12-months diaries were AUS$ 3,330 ± 2,887. There were no significant differences between the 12-months data and extrapolated 1, 3 and 6-months diaries (t-tests; p = 0.17, 0.89 and 0.73, respectively). However, the 1-month variation was substantially larger (SD ± 5860) compared to the 3-month and 6-month variances (SD ± 3037 and 3030, respectively) for total costs. Also, compared to the 12-months diaries, the 1-month data consistently recorded the weakest correlation coefficients for all cost categories compared to the other time intervals. Conclusions: Given that diary completion can be particularly challenging for individuals with impaired vision, a minimum 3-months data collection period can provide reliable estimates of annual costs associated with vision impairment.