Study sample Power calculations to determine the sample size were performed (apparently in the preliminary phase of the study). These suggested that a sample of 99 patients in each group was required to detect a 0.4 difference in mean scores between the two groups with 80% power and at a 5% level of significance. All of the patients who underwent bilateral implantation of the multifocal IOL were eligible for the study. Of the 126 patients identified, 110 (87%) agreed to participate and were enrolled in the study. A comparison group of 142 patients, who were implanted bilaterally with a monofocal IOL at the same sites as the multifocal patients, met the study criteria and were invited to participate as a control group. Of these, 112 agreed to participate. Reasons for refusal were not stated.