Age-related Differential Item Functioning for the Patient-Reported Outcomes Information System (PROMIS®) Physical...

Area of Science:

• Gerontology
• Health Outcomes Research
• Psychometrics

Background:

• The Patient-Reported Outcomes Measurement Information System (PROMIS) is a vital tool for assessing health status.
• Physical functioning is a key health outcome, but its measurement may vary across age groups.
• Ensuring item bank equivalence across different demographics is crucial for accurate health assessments.

Purpose of the Study:

• To evaluate the psychometric equivalence of the PROMIS wave 1 physical functioning item bank.
• To compare item performance between adults aged 50 years and older versus those aged 18-49 years.
• To identify potential age-related biases in physical functioning item responses.

Main Methods:

• Administered 114 physical functioning items with 5 response choices to English and Spanish-speaking adults.
• Analyzed item frequencies, means, standard deviations, item-scale correlations, and internal consistency reliability.
• Evaluated Differential Item Functioning (DIF) by age using an R-squared criterion of 0.02 or above.

Main Results:

• Thirty out of 114 items (26%) were flagged for DIF based on the specified criterion.
• Respondents aged 18-49 generally reported higher expected total scores compared to those aged 50 or older.
• Significant age-based response differences were observed in a substantial portion of the physical functioning items.

Conclusions:

• Age is a significant factor influencing responses to items in the PROMIS physical functioning bank.
• Thirty items demonstrated differential item functioning (DIF) between younger and older adult groups.
• This study highlights the need to consider age-specific interpretations of physical functioning measures within the PROMIS item bank.