The following clinical parameters are evaluated: age, gender, ocular and systemic comorbidities, educational level, preoperative and postoperative monocular distance uncorrected visual acuity (UVA), distance best spectacle-corrected visual acuity (BSCVA) of the eye for cataract surgery, binocular distance UVA and BSCVA, refraction, spherical equivalent (SE), and intraocular pressure.

DIF indicates the differences between different subgroups of patients, since the questionnaire item calibration should be comparable across different patient groups. DIF occurs if patients from different subgroups with the same underlying true ability have an unequal probability of giving of a response to an item. DIF is assessed by evaluating age, gender, existence of ocular comorbidities, first vs second eye cataract surgery and binocular distance BSCVA. DIF of >1.0 logits is significant, DIF with values between 0.5 and 1.0 is minimal, and DIF <0.5 logits is considered absent.

Τargeting of the questions to the patient sample, which indicates how well the items' difficulties match the person ability, is assessed to establish if the questions are appropriate for patients before and following cataract surgery. This can be assessed graphically by observing the spread along the person-item map and by the difference between the item and the person mean values. A well-targeted instrument requires the ability of the patients and the difficulty of the questions to be centered on the same mean (targeting of 0). In general, a mean difference in magnitude of ≥1 logit indicates significant mistargeting, while a difference of <1.0 logit indicates good targeting, with targeting of 0 being ideal. A positive value indicates that the items are too difficult relative to person's ability, while a negative value indicates that the items are too easy. A person-item map also visualizes the item hierarchy of difficulty, ranging from a minimum to maximum difficulty of performance.