Variation in the readability of items within surveys.

The objective of this study was to estimate the variation in the readability of survey items within 2 widely used health-related quality-of-life surveys: the National Eye Institute Visual Functioning Questionnaire-25 (VFQ-25) and the Short Form Health Survey, version 2 (SF-36v2). Flesch-Kincaid and Flesch Reading Ease formulas were used to estimate readability. Individual survey item scores and descriptive statistics for each survey were calculated. Variation of individual item scores from the mean survey score was graphically depicted for each survey. The mean reading grade level and reading ease estimates for the VFQ-25 and SF-36v2 were 7.8 (fairly easy) and 6.4 (easy), respectively. Both surveys had notable variation in item readability; individual item readability scores ranged from 3.7 to 12.0 (very easy to difficult) for the VFQ-25 and 2.2 to 12.0 (very easy to difficult) for the SF-36v2. Because survey respondents may not comprehend items with readability scores that exceed their reading ability, estimating the readability of each survey item is an important component of evaluating survey readability. Standards for measuring the readability of surveys are needed.