The term Differential Item Functioning (DIF) refers to questions that are relatively easier or more difficult to answer for different groups of people who are matched on ability. When this happens, the probability of correctly answering is not exclusively explained by the personal relative ability (i.e. subject’s ability over question’s difficulty), but also by other factors, such as gender, socio-economic status, and so on. Unlike previous studies about the gender gap, this paper is not aimed at comparing male and female students’ performance from a substantive standpoint, but instead is mainly aimed at controlling question items’ functionality. This investigation plays a key role in developing an achievement test because, when DIF occurs, the local independence (one of the main properties of the Rasch model) is violated. In order to achieve this goal, we compared the items’ location order along the latent trait, both in male and female group. Given the aim of this study, our methodological approach could be more fruitfully implemented in pre-testing phase, but, in order to illustrate it, we applied our strategy to the Italian census data gathered by INVALSI (Italian National Institute for Educational Evaluation) in 2013. The data matrix included 484.279 pupils who attend the 5th grade level of elementary school.
|Keywords:||Differential Item Functioning (DIF), Rasch Model, Gender Gap, Students’ Achievement, Testing Instruments’ Development, Pre-testing|
Researcher, Italian National Institute for Educational Evaluation, Rome, Italy