Detecting differential item functioning (DIF) in the diabetes risk perception survey (RPS-DM)

Jason Fletcher, Fordham University


Differential Item Functioning (DIF) occurs when item performance differs between groups matched on the latent construct bring measured. Differential performance of items between ethnic groups has been shown to impact assessments of health outcomes, such as quality of life (QoL), subjective well-being and coping styles and self-report mental health and depression inventories. The Risk Perception Survey for Diabetes Mellitus (RPS-DM) consists of 31 questions and provides scale scores reflecting (1) risk knowledge, (2) perceived personal control, (3) worry, (4) optimism, (5) personal and (6) environmental disease risk. Items of the RPS-DM composite risk score were evaluated for DIF occurring between Hispanic and non-Hispanic respondents using Samejima's Graded Response Model. Likelihood ratio tests based on item response theory (IRT) were used to detect item-level DIF. DIF magnitude was quantified using standardized mean difference (SMD). SMD and the results of significance tests were combined to classify items as having negligible (AA), weak (BB) or strong (CC) DIF. These analyses indicated that the majority of items (12 of 18) were classified as having negligible DIF. Those that were impacted by non-negligible DIF were examined for content. This revealed that after being matched on overall perceived risk, Hispanic respondents reported greater perceived risk from environmental sources (violent crime, illicit drugs and secondhand smoke), and non-Hispanic respondents reported greater perceived risk of developing disease and risk from medical sources (high blood pressure, stroke and risk from medical tests). It is hypothesized these results may reflect differences in socioeconomic and disease awareness between the groups. Despite these findings, there is cancellation of item-level DIF when calculating the composite score, suggesting the use of the composite score is appropriate to measure perceived risk in multi-ethnic populations.

Subject Area

Quantitative psychology|Hispanic American studies

Recommended Citation

Fletcher, Jason, "Detecting differential item functioning (DIF) in the diabetes risk perception survey (RPS-DM)" (2009). ETD Collection for Fordham University. AAI3353768.