Exploring the Internal Structure of the NHANES Physical Functioning Questionnaire

Abstract

Function is an important health outcome that has been associated with patient hospitalization, nursing home admission, falling, level of dependency, and death in adults. The Physical Functioning Questionnaire (PFQ) of the National Health and Nutrition Examination Survey (NHANES) is used to measure functional limitations in Americans with disabilities. However, little is known about the internal structure of this scale. PURPOSE: To evaluate the internal structure of the 20-item NHANES PFQ. METHODS: Data from the 2011 to 2012 NHANES were analyzed for this study. 1620 adults (mean age 61.37±15.50) who provided responses to all PFQ items were included in the analyses. Prior to analysis the sample was divided into two groups using an odd/even split to allow for cross-validation of the model. An exploratory factor analysis (EFA) was conducted to identify the internal factor structure and remove poor items. The model was then tested using confirmatory factor analysis (CFA). Chi-square goodness of fit test, comparative fit index (CFI), and root mean square error of approximation (RMSEA) model fit indices were used to determine model fit. RESULTS: Parallel analysis revealed a max of 4-factors due to random chance alone. Using scree plot analysis, eigenvalues >1, and cumulative variance explained, a 3-factor model was identified from the data. Two of the items (“difficulty walking between rooms on the same floor” and “difficulty reaching overhead”) displayed poor item communalities (<.35) and did not load well on any factors. These items were removed which significantly improved the overall variance explained by the model (53.00%). The 3-factors identified were: “gross-motor activities of daily living (ADL),” “Participation and the Environment” and “fine-motor ADL.” The CFA showed that the 3-factor model had acceptable fit indices (Χ2 = 463.90, df =109 p <.001; CFI = 0.940; RMSEA=.063), thus confirming the latent variable structure emerged in the EFA. CONCLUSIONS: Although two of the items were not supported by the model; the results from this study provide evidence for the use of the PFQ with the NHANES. Additionally, the model identified appears to be in line with the model proposed by the World Health Organization.