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

Peter D Hart

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 ps 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.

Highlights

[1] The proper assessment of Physical functioning (PF) is important to health professionals due to the strong links between PF and injury, illness, and mortality. [2,3,4] Several objective measures of PF are used in research and practice and include grip strength, walking speed, chair raises, and standing balance tests
item response theory (IRT) models can assess the functioning of each item to determine how well they perform in measuring the trait of interest
The IRT analysis resulted in 8 well-fitting items with large item discrimination, moderate item difficulty range, and adequate item fit (RMSEAs < .036)

Summary

Introduction

Physical functioning (PF) is the ability to engage in daily activities of varying importance. [1] The proper assessment of PF is important to health professionals due to the strong links between PF and injury, illness, and mortality. [2,3,4] Several objective measures of PF are used in research and practice and include grip strength, walking speed, chair raises, and standing balance tests. [5] When direct participant examination is not possible, a very popular PF assessment alternative is the use of self-reported assessments. Classical test theory (CTT) is the most common and conventional model used by researchers to validate self-reported scales. A more modern approach to scale development and validation, which can complement CTT-based research, is item response theory (IRT). IRT provides a system of mathematical equations which can model the relationship between latent traits and observed responses to items.. The purpose of this study was to firstly use IRT to create a brief PF scale (BPFS) and secondly to examine the relationship between BPFS scores and several different health characteristics. This study used item response theory (IRT) to create a brief PF scale (BPFS) and subsequently examined its relationship with several health characteristics. 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

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Results

Conclusion