2. An IRT scale was originally developed using 22 items with explicit economic content administered to IEA samples of 17-year-olds in 15 countries
in 2000 (Amadeo et al., 2002). Since the United States and several other countries did not participate in the part of the study where 17-year-olds were
tested, the scores of 14-year-olds were estimated with standard IRT methodology using anchor items that linked the two tests; 12 items with explicit and
implicit economic content were included (Husfeldt, 2003).
3. A 13-item IRT scale developed from the CIVED assessment by Schulz and Sibberns (2004). Skills items were differentiated from content knowledge
items based on a confrmatory factor analysis