Figure 2
From: Rasch analysis for development and reduction of Symptom Questionnaire for Visual Dysfunctions (SQVD)
Person-item map for the SQVD. Patients are represented on the left of the dashed line by the symbol "#" (which represents 2 subjects) and "." (which indicates 1 subject). On the right of dashed line are illustrated the items of SQVD 14-item version with their number (Pnumber of item). M indicates the mean measure (on the left the person ability and on the right the item difficulty). S shows one standard deviation from the mean and T denotes two standard deviations. Higher ability for persons (higher frequency of symptoms) and more difficult items are on the top of the figure.
