Different positions of items in booklets affect the probabilities of correct answers. This effect is called the item position effect in the literature, which causes variances in the item and person parameters. The aim of this study is to investigate the item position effect within the framework of explanatory item response theory. The analyses of this research were carried out on the PISA 2015 Turkey sample, and the item position effect was examined in the domains of reading and mathematics. In addition, the effect of the item position in different item formats (open response and multiple choice) was investigated. According to the results, the item position effect decreased the probability of answering the item correctly, and this effect was higher in reading than in mathematics. Furthermore, in the domain of mathematics, open response items were affected more than multiple-choice items by the item position. In the reading domain, open response and multiple choice items were affected similarly. The results of the analysis show that there were undesirable effects of the item position, and these effects should be taken into account.