Item Analysis of Functional Measure Indicators in the National Health and Nutrition Examination Survey: A Cross-sectional Study.

OBJECTIVE

This study aimed to develop a function, activities, and participation measurement scale using the questions on the National Health and Nutrition Examination Survey (NHANES) by applying item response theory approaches.

DESIGN

This was a cross-sectional study.

PARTICIPANTS

Survey data were collected from 2512 participants within the NHANES.

METHODS

Twenty questions from the NHANES physical functioning section were included. Exploratory and confirmatory factor analyses were conducted to evaluate the factorial structure and model fit of the NHANES instrument. A multidimensional Rasch modeling was used to model the response data after confirming its model fit. To assess validity across subgroups, differential item functioning test was conducted with respect to sex and race using the three-dimensional partial credit model.

RESULTS

Item fit indices indicated a good fit (root-mean-square error of approximation = 0.049, standardized root-mean-square residual = 0.052, Tucker-Lewis index = 0.975). Rasch analysis indicated that "stoop/crouch/kneel," "stand for long periods," and "push/pull large objects" were the three most difficult items, whereas "walk between rooms," "use fork/knife," and "leisure at home" were the easiest. The measure demonstrated good internal consistency overall (Cronbach α = 0.90).

CONCLUSION

The NHANES function, activities, and participation measure demonstrates sufficient evidence of reliability, internal consistency, and validity in noninstitutionalized community-dwelling population.

TO CLAIM CME CREDITS

Complete the self-assessment activity and evaluation online at http://www.physiatry.org/JournalCME.

CME OBJECTIVES

Upon completion of this article, the reader should be able to (1) Recognize the potential benefits of using validated patient-reported functional outcome measures within the publically available National Health and Nutrition Examination Survey (NHANES) data for rehabilitation research; (2) Describe the process of scale development and validation; (3) Identify item difficulty based on the item difficulty distribution; and (4) Identify the applicability of the measure to different population groups based on differential item functioning.

LEVEL

Advanced.

ACCREDITATION

The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.The Association of Academic Physiatrists designates this Journal-based CME activity for a maximum of 1.0 AMA PRA Category 1 Credit(s) ™. Physicians should only claim credit commensurate with the extent of their participation in the activity.