An IRT-constructed Brief Physical Functioning Scale and Its Association with Health Status

Peter D. Hart^1,

¹Health Promotion Research, Havre, MT 59501

Cite this paper

Peter D. Hart. An IRT-constructed Brief Physical Functioning Scale and Its Association with Health Status. American Journal of Public Health Research. 2020; 8(6):184-189. doi: 10.12691/AJPHR-8-6-1

Abstract

Background: This study used item response theory (IRT) to create a brief PF scale (BPFS) and subsequently examined its relationship with several health characteristics. Methods: Data were used from N=1,716 adults 50+ years of age participating in a large health survey. A pool of 19 PF items were dichotomized to either 1 (any amount of difficulty) or 0 (no difficulty). A 2-parameter logistic (2PL) IRT model was used to evaluate item fit to the unidimensional PF construct. Criteria used to eliminate an item was 1) a small discrimination (slope) parameter, 2) a significant chi-square statistic for cell residuals, and 3) a large root mean square error of approximation (RMSEA). The IRT model was continually re-fitted until all remaining items met criteria. SAS PROC IRT and R ltm were used for scale construction. Results: The IRT analysis resulted in 8 well-fitting items with large item discrimination (as > 2.03), moderate item difficulty range (bs: -0.07 - 1.35), and adequate item fit (RMSEAs < .036). After full adjustment, each additional BPFS point significantly (ps < .05) increased stepwise the odds of reporting poor HRQOL (OR = 1.59), being depressed (OR = 1.46), having thoughts of suicide (OR = 1.35), not meeting PA guidelines (OR = 1.29), being BMI-obese (OR = 1.23), being WC-obese (OR = 1.13), experiencing poor sleep (OR = 1.29), and reporting sleepiness (OR = 1.16). Conclusion: Results from this study show that the IRT-constructed BPFS is an efficient and valid tool that can predict health status in older adults.

Keywords

physical functioning, Item response theory (IRT), psychometrics, aging and health

Copyright

This work is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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