Impact of unbalanced DIF item proportions on group-specific DIF identification

Abstract

Differences in type I error and power rates for majority and minority groups are investigated when differential item functioning (DIF) contamination in a test is unbalanced. Typically, type I error and power rates are aggregated across groups, however cumulative results can be misleading if subgroups are affected differently by study conditions. With unbalanced DIF contamination, type I error and power rates are reduced for groups with more DIF items favoring them, and increased for groups with less DIF contamination. Even when aggregated impacts appear small, differing subgroup impacts can result in a larger proportional bias than in the original data.

Keywords:

• Differential item functioning
• contamination
• unbalanced DIF
• test validity