The Programme for International Student Assessment (PISA) index of comfort with and perceived ability to use computers was derived from students’ responses to the following questions: How comfortable are you with using a computer?; How comfortable are you with using a computer to write a paper?; How comfortable are you with taking a test on a computer?; and, If you compare yourself with other 15-year-olds, how would you rate your ability to use a computer? For the first three questions, a four-point scale was used with the response categories ‘very comfortable’, ‘comfortable’, ‘somewhat comfortable’ and ‘not at all comfortable’. For the last questions, a four-point scale was used with the response categories ‘excellent’, ‘good’, ‘fair’ and ‘poor’. The indices were derived using the WARM estimator. For information on the conceptual underpinning of the index see Eignor et al. (1998).