A substantial proportion of the PISA 2009 items were open-ended and required coding by trained personnel. It was important therefore that PISA implemented procedures which maximised the validity and consistency (both within and between countries) of this coding. Each country coded items on the basis of coding guides prepared by the Consortium (see Chapter 2) using the design described in Chapter 6. Training sessions to train coders from different countries on the use of the coding guides were held prior to both the field trial and the main survey.