Measuring neurobehavioral functioning in people with traumatic brain injury: Rasch analysis of Neurobehavioral Functioning Inventory.

Objective:
To examine internal construct validity of the Neurobehavioral Functioning Inventory (NFI) by applying Rasch analysis.

Setting:
An outpatient rehabilitation program trial in New Zealand employing a goal-setting intervention in people with traumatic brain injury (TBI).

Participants:
One hundred eight people (mean age = 46 years; 73% male) between 6 months and 5 years post-TBI.

Design:
Rasch analysis of the NFI (Partial Credit Model).

Results:
Three NFI subscales were not unidimensional and at least 4 items in each subscale had disordered response categories. Two items showed differential item functioning by age, 1 item by educational attainment, and 2 items were found to misfit the overall construct. These items were excluded from the total score calculation. The revised scale fit the Rasch model and supported the internal construct validity of the NFI.

Conclusions:
Current scoring of the NFI subscales for people with TBI in New Zealand does not meet the requirements of the Rasch model. The revised version of NFI can improve the interpretation of scores but should be further tested with people with TBI in other settings.