Age-related Differential Item Functioning for the Patient-Reported Outcomes Information System (PROMIS®) Physical Functioning Items.
OBJECTIVE
To evaluate the equivalence of the PROMIS® wave 1 physical functioning item bank, by age (50 years or older versus 18-49).


METHODS
A total of 114 physical functioning items with 5 response choices were administered to English- (n=1504) and Spanish-language (n=640) adults. Item frequencies, means and standard deviations, item-scale correlations, and internal consistency reliability were estimated. Differential Item Functioning (DIF) by age was evaluated.


RESULTS
Thirty of the 114 items were fagged for DIF based on an R-squared of 0.02 or above criterion. The expected total score was higher for those respondents who were 18-49 than those who were 50 or older.


CONCLUSIONS
Those who were 50 years or older versus 18-49 years old with the same level of physical functioning responded differently to 30 of the 114 items in the PROMIS® physical functioning item bank. This study yields essential information about the equivalence of the physical functioning items in older versus younger individuals.
UCLA Division of General Internal Medicine and Health Services Research, Department of Medicine, 911 Broxton Avenue, Los Angeles, CA 90095-1736, USA.
Sylvia H
SH
Paz
Karen L
KL
Spritzer
Leo S
LS
Morales
Ron D
RD
Hays
Differential Item Functioning (DIF); Item Response Theory (IRT); Physical function; Survey Research