Empirical analysis of the International Classification of Functioning, Disability and Health (ICF) using structural equation modeling

Abstract

Objective:: To empirically test the relationships proposed by the International Classification of Functioning, Disability and Health (ICF) among its domains.

Method:: The cross-sectional study was completed with 226 adult patients with different health conditions who attended a Brazilian rehabilitation unit. The ICF components were measured with the following instruments: World Health Organization Disability Assessment Instrument II, Functional Independence Measure, Participation Scale, Craig Hospital Inventory of Environmental Factors, and a protocol designed to gather information on body structure and function and personal factors.

Results:: Structural equation modeling showed good model adjustment, GFI=0.863; AGFI=0.795; RMSEA=0.028 (90% CI=0.014-0.043). Significant relationships were found between activity and both body structure and function (standard coefficient=0.32; p<0.0001) and participation components (standard coefficient=–0.70; p<0.0001). Environmental and personal factors had a significant effect on the three functioning components (standard coefficient =0.39; p<0.0001; standard coefficient =-0.35; p<0.001, respectively). In contrast, body structure and function had no significant effect on participation (standard coefficient=–0.10; p=0.111) and health conditions had no significant effect on any of the functioning components, i.e., body structure and function, activity, and participation (standard coefficient=–0.12; p=0.128).

Conclusion:: Some of the ICF’s proposed relationships across domains were confirmed, while others were not found to be significant. Our results reinforce the contextual dependency of the functioning and disability processes, in addition to putting into perspective the impact of health conditions.

Figure 1. Schema diagram indicating the instrumentation used to measure the different domains of the ICF. Source: Figure adapted from the WHO.

Figure 2. Graphic representation of the structural equation models exploring the relationships among factors representing components of the ICF model. Paths labeled with a “1” were used solely for identification and were therefore not tested. Ovals indicate latent constructs, while rectangles indicate subjacent constructs (i.e., the observed variables). Error values associated with each indicator are shown in small circles labeled with the letter “e”. Standard coefficients are shown above the structural paths between the latent constructs. Standard factorial loads are indicated between the latent constructs and the indicators. Residual errors associated with each latent variable are shown in small circles labeled with the letter “r”. Figure legends: 6MWT: six minute walking test; activeorretired: active at work or retired; age: age in years; alcoholconsumption: regular consumption of alcoholic beverage; vas: visual analog scale; bmi: body mass index; bsf: body structure and function; chieff: frequency of Craig Hospital Inventory of Environmental Factors; chiefm: magnitude of Craig Hospital Inventory of Environmental Factors; children: number of children; education: years of education; ef: environmental factors; function: integration of the components body structure and function, activity, and participation; fim: Functional Independence Measure; ftf: Fingers-to-Floor Test; habitsmoking: smoking; hc: health condition; income: annual income; lgs: left upper limb grip strength; marital: patient is living with partner; pf: personal factors; physicalactivity: regular practice of physical activity; ps: Participation Scale; rgs: right upper limb grip strength; sei: Socioeconomic Index of Occupations; sst: Sit-to-Stand Test; sex: sex of participants; tbs: Back Scratch Test; whodas: World Health Association Disability Assessment Instrument II.

Figure 3. Structural equation model of the relationships between functioning components from the ICF model (n=226; chi-square = 124.1; df=19; GFI=0.886; AGFI=0.781; RMSEA=0.057 [90% CI = 0.031-0.084]). Figure legends: vas: visual analog scale; bsf: body structure and function; fim: Functional Independence Measure; lgs: left upper limb grip strength; ps: Participation Scale; sixmwt: six minute walking test; sst: Sit-to-Stand Test; tbs: Back Scratch Test; WHODAS: World Health Association Disability Assessment Instrument II. The decimal numbers on the arrows indicate the significant correlation coefficients from the Structural Equation Modeling, showing positive and negative (-) associations.

Figure 4. Results of the structural equation model of the complete model of the ICF (n=226; chi square = 252.9; df = 52; GFI=0.863; AGFI=0.795; RMSEA=0.028 [90% CI=0.014-0.043]). Figure legends: age: age in years; alcoholconsumption: regular consumption of alcoholic beverage; vas: visual analog scale; chieff: frequency of Craig Hospital Inventory of Environmental Factors; chiefm: magnitude of Craig Hospital Inventory of Environmental Factors; ef: environmental factors; education: years of education; function: integration of the components body structure and function, activity, and participation; fim: Functional Independence Measure; pf: personal factors; ps: Participation Scale; sei: Socioeconomic Index of Occupations; sex: sex of participants; sixmwt: six minute walking test; whodas: World Health Association Disability Assessment Instrument II. The decimal numbers on the arrows indicate the significant correlation coefficients from the Structural Equation Modeling, showing positive and negative (-) associations.