We also completed an analysis of differential item functioning (DIF, or “item bias”) by age, gender, and visual acuity. None of the Perceived Stress Scale items exhibited evidence of significant DIF (greater than 0.5 logits) by gender. Two items, “I felt nervous or stressed” (0.54 logits) and “I felt on top of things” (0.63 logits) showed some evidence of DIF by age. Younger participants found it easier to endorse the “I felt nervous or stressed” item and more difficult to endorse the “I felt on top of things” item than participants above the median age. Two items, “I was upset by things that normally do not upset me” (0.59 logits) and “I felt things were going my way” (0.64 logits) showed some evidence of DIF by better-eye visual acuity. Participants with visual acuity worse than the median value found it easier to endorse the “I was upset by things that normally do not upset me” item and also the “I felt things were going my way” item. There was no significant correlation between better-eye visual acuity and Perceived Stress Scale person measure (r = −0.04, P = .06).
Bradley E. Dougherty
338 W. 10th Ave
Supported by National Eye Institute/National Institutes of Health, Department of Health and Human Services grant K23EY022940.
Received May 16, 2016; accepted November 15, 2016.
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