The Effect of Ratio of Items Indicating Differential Item Functioning on Computer Adaptive and Multi-Stage Tests

Abstract

Recently, adaptive test approaches have become a viable alternative to traditional fixed-item tests. The main advantage of adaptive tests is that they reach desired measurement precision with fewer items. However, fewer items mean that each item has a more significant effect on ability estimation and therefore those tests are open to more consequential results from any flaw in an item. So, any items indicating differential item functioning (DIF) may play an important role in examinees' test scores. This study, therefore, aimed to investigate the effect of DIF items on the performance of computer adaptive and multi-stage tests. For this purpose, different test designs were tested under different test lengths and ratios of DIF items using Monte Carlo simulation. As a result, it was seen that computer adaptive test (CAT) designs had the best measurement precision over all conditions. When multi-stage test (MST) panel designs were compared, it was found that the 1-3-3 design had higher measurement precision in most of the conditions; however, the findings were not enough to say that 1-3-3 design performed better than the 1-2-4 design. Furthermore, CAT was found to be the least affected design by the increase of ratio of DIF items. MST designs were affected by that increment especially in the 10-item length test.