Functional ability is an important outcome indicator of healthy ageing. Measuring this indicator helps to identify populations with potentially greater needs for support and resources, thereby informing policy and intervention strategies aimed at promoting healthy aging and enhancing the quality of life for older people.
Definition:
This indicator measures the percentage of older who exhibit higher levels of functional ability, which encompasses ability to meet basic needs, learn, grow, make decisions, be mobile, build and maintain relationships, and contribute to society.
Disaggregation:
Age (five-year age band), sex, income level, education level, place of residence (administrative region, e.g. cities, towns, semi-dense areas, and rural areas), setting (residential care facility, at home in the community), disability status, nationally relevant population groups
Method of measurement
This indicator is taken from representative survey data by deriving a latent functional ability score from a predefined set of items spanning the five functional ability domains in the WHO healthy ageing framework: meeting basic needs, learning growth and decision-making, mobility, building and maintaining relationships, and contribution to family and society. Items are selected and grouped into these five domains using a pre-specified psychometric protocol, and item coding is harmonised so that higher values consistently indicate higher functional ability. Items are then modelled according to their measurement level using item response theory, with dichotomous items specified using a two-parameter logistic model and ordinal items specified using a graded response model. A bifactor model is fitted in which a general functional ability factor loads on all included items, alongside five domain-specific factors corresponding to the five functional ability domains. Respondent-level factor scores are generated using an expected a posteriori scoring approach to produce a general functional ability score and domain scores, and scores are transformed to a 1–100 metric for reporting. High functional ability is defined by anchoring the classification to a separate wellbeing measure. A wellbeing score (WHO Wellbeing 5 scale) is computed using the selected wellbeing instrument, and ""high wellbeing"" is defined using an established threshold for that instrument. A receiver operating characteristic analysis is then conducted with the rescaled general functional ability score as the classifier and high wellbeing as the external criterion. The cut-point on the functional ability score is selected using a predefined optimisation rule and validated using internal validation procedures to support stability. The numerator comprises older people whose general functional ability score meets or exceeds the wellbeing-anchored cut-point, and the denominator comprises older people with sufficient valid item data to generate a functional ability score under the model. Prevalence estimates are produced using survey sampling weights and accounting for complex survey design, and estimates may be age- and sex-standardised to support comparisons across populations.
Note: Because the cut-point is wellbeing-anchored, the wellbeing measure and its threshold need to be specified consistently across settings, and this approach should be tested in future validation studies to confirm reliability and cross-context comparability.
Other possible data sources:
Population census
Household surveys
Preferred data sources:
Published nationally-representative population-based surveys
This indicator relies on survey-based measures across multiple functional ability domains, several of which are derived from self-reported responses. Self-reported data may be affected by recall bias, social desirability bias, and differences in how respondents interpret questions about daily functioning, relationships, and contribution to society. Cultural and contextual differences in expectations of independence, participation, and social roles may also influence how respondents report their abilities, which can affect cross-country comparability.
The construction of the functional ability score uses a latent variable approach based on item response theory. Although this approach allows the integration of diverse indicators into a single composite measure, the results depend on the quality of the underlying data, the selection of items included in the model, and the assumptions of the psychometric model. Differences in survey instruments, item wording, and data collection procedures across countries may affect measurement equivalence and comparability of the resulting scores.
In addition, the threshold used to define high functional ability is anchored to a wellbeing measure (WHO-5), using receiver operating characteristic analysis. While this approach provides an external reference for determining a meaningful cut-point, the resulting threshold may be sensitive to the characteristics of the study population and may not generalize across different cultural, socioeconomic, or health contexts. Because the indicator is currently classified as Tier III, further validation in cross-country studies is required to assess the robustness of the measurement approach, confirm the stability of the cut-point, and ensure comparability of estimates across populations and over time.
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