DIF as a pedagogical tool
Analysis of item characteristics in ICILS to understand what students are struggling with
International large-scale assessments like international computer and information literacy study (ICILS) (Fraillon et al. in International Association for the Evaluation of Educational Achievement (IEA), 2015) provide important empirically-based knowledge through the proficiency scales, of what characterizes tasks at different difficulty levels, and what that says about students at different ability levels. In international comparisons, one of the threats against validity is country differential item functioning (DIF), also called item-by-country interaction. DIF is a measure of how much harder or easier an item is for a respondent of a given group as compared to respondents from other groups of equal ability. If students from one country find a specific item much harder or easier than students from other countries, it can impair the comparison of countries. Therefore, great efforts are directed towards analyzing for DIF and removing or changing items that show DIF. From another angle, however, this phenomenon can be seen not only as a threat to validity, but also as an insight into what distinguishes students from different countries, and possibly their education, on a content level, providing even more pedagogically useful information. Therefore, in this paper, the data from ICILS 2013 is re-analyzed to address the research question: Which kinds of tasks do Danish, Norwegian, and German students find difficult and/or easy in comparison with students of equal ability from other countries participating in ICILS 2013? The analyses show that Norwegian and Danish students find items related to computer literacy easier than their peers from other countries. On the other hand, Danish and, to a certain degree, Norwegian students find items related to information literacy more difficult. Opposed to this, German students do not find computer literacy easier, but they do seem to be comparably better at designing and laying out posters, web pages etc. This paper shows that essential results can be identified by comparing the distribution of difficulties of items in international large-scale assessments. This is a more constructive approach to the challenge of DIF, but it does not eliminate the serious threat to the validity of the comparison of countries.