Objectives: To evaluate the measurement structure of the ICOPE screening tool (IST) of intrinsic capacity and to find out whether the IST as a global measure adds explanatory power over and above its domains in isolation to predict the occurrence of adverse health outcomes such as dependence and hospitalization in community-dwelling older people.
Design: Secondary analysis of a cohort study, the Toledo Study of Healthy Ageing.
Setting: Province of Toledo, Spain.
Participants: Community-dwelling older people.
Measurements: Items equal or similar to those of the IST were introduced as a reflective-formative construct in a Structural Equation Model to evaluate its measurement structure and its association with dependence for basic and instrumental activities and hospitalization over a three-year period.
Results: A total of 1032 individuals were analyzed. Mean age was 73.5 years (sd 5.4). The least preserved indicators were ability to recall three words (18%) and to perform chair stands (54%). Vision and hearing items did not form a single sensory domain, so six domains were considered. Several cognition items did not show sufficiently strong and univocal associations with the domain. After pruning the ill-behaved items, the measurement model fit was excellent (Satorra-Bentler scaled chi-square: 10.3, degrees of freedom: 11, p=0.501; CFI: 1.000; RMSEA: 0.000, 90% CI: 0.000-0.031, p value RMSEA<=0.05: 1; SRMR: 0.055). In the structural model, the cognition domain items were not associated as expected with age (p values 0.158 and 0.293), education (p values 0.190 and 0.432) and dependence (p values 0.654 and 0.813). The IST included as a composite in a model with the individual domains showed no statistically significant associations with any of the outcomes (dependence for basic activities: 0.162, p=0.167; instrumental: -0.052, p=0.546; hospitalization: 0.145, p=0.167), while only the mobility domain did so for dependence (basic: -0.266, p=0.005; instrumental: -0.138, p=0.019). The model fit of the last version was good (Satorra-Bentler scaled chi-square: 52.1, degrees of freedom: 52, p=0.469; CFI: 1.000; TLI: 1.000; RMSEA: 0.01, 90% CI: 0.000-0.02, p value RMSEA<=0.05: 1; SRMR: 0.071). The IST operationalized as the sum of non-impaired domains was not associated after covariate adjustment (dependence for basic activities: -0.065, p=0.356; instrumental: -0.08, p=0.05; hospitalization: -0.003, p=0.949) either.
Conclusion: The cognitive domain of the IST, and probably other of its items, may need a reformulation. A global measure of intrinsic capacity such as the IST does not add explanatory power to the individual domains that constitute it. So far, our results confirm the importance of checking the findings of the IST with a second confirmatory step, as described in the WHO's ICOPE strategy.
Keywords: ICOPE; Intrinsic capacity; dependence; domains; hospitalization.