Alireza Ahmadi - Shiraz University, Iran
Touraj Jalili - Shiraz University; PhD Candidate, University of Isfahan, Iran

The  present  study  aimed  at  investigating  DIF  sources  on  an  EFL  reading  comprehension test.  Accordingly,  ۲  DIF  detection  methods,  logistic  regression  (LR)  and  item  response theory  (IRT),  were  used  to  flag  emergent  DIF  of  ۲۰۳  (۱۱۰  females  &  ۹۳  males)  Iranian EFL examinees’ performance on a reading comprehension test. Seven hypothetical DIF sources were examined in this regard: text familiarity, gender, topic/text interest, guessing, and  the  social  variables  of  location,  income,  and  educational  status.  Only  LR,  for  gender and  text  familiarity,  could  preempt  DIF  with  gender  supporting  the  gendered-text  effect while  text  familiarity  benefiting,  inversely,  the  participants  with  low  level  of  text familiarity.  For  interest  in  topic,  LR  found  a  single  item  favoring  the  group  with  higher levels  of  interest  and  the  IRT  model  detected  DIF  in  either  extreme.  Regarding  guessing and  income,  the  LR  indicated  DIF  supporting  the  low  guessers  and  high-income  group whereas IRT, conversely,  showed DIF  favoring the high guessers and low-income  group. For  location  and  education  both  methods,  correspondingly,  demonstrated  DIF  for  the expensive  location  and  educated  groups.  Finally,  the  differential  test  functioning  result made it clear that only three sources of DIF (gender, income, & interests) were transferred to the test level. The findings could support a proportional effect of DIF sources.

DIF, LR, IRT, Reading Comprehension