Purpose: To validate the Perceived Stress Scale (PSS) in patients with age-related macular degeneration (AMD) using Rasch analysis.
Methods: Study participants with AMD were recruited from the retina service of the Department of Ophthalmology at the Ohio State University during clinical visits for treatment or observation. Visual acuity with habitual distance correction was assessed. A 10-item version of the PSS was administered in large print or by reading the items to the patient. Rasch analysis was used to investigate the measurement properties of the PSS, including fit to the model, ability to separate between people with different levels of perceived stress, category response structure performance, and unidimensionality.
Results: A total of 137 patients with a diagnosis of AMD were enrolled. The mean (±SD) age of participants was 82 ± 9 years. Fifty-four percent were female. Median Early Treatment of Diabetic Retinopathy Study (ETDRS) visual acuity of the better eye was 65 letters (Snellen 20/50), with a range of approximately 20/800 to 20/15. Forty-seven percent of participants were receiving an anti-VEGF injection on the day of the study visit. The response category structure was appropriate. One item, “How often have you felt confident in your ability to handle your personal problems?” was removed due to poor fit statistics. The remaining nine items showed good fit to the model, acceptable measurement precision as assessed by the Rasch person separation statistic, and unidimensionality. There was some evidence of differential item functioning by age and visual acuity.
Conclusions: The Perceived Stress Scale demonstrated acceptable measurement properties and may be useful for the measurement of perceived stress in patients with AMD.
The Ohio State University College of Optometry (BED, S-SLC), and The Ohio State University Department of Ophthalmology (FHD), Columbus, Ohio.
Bradley E. Dougherty, The Ohio State University College of Optometry, 338 W. 10th Ave, Columbus, OH 43210, e-mail: email@example.com