Table 1.

Measures, definitions and operationalizations of multimorbidity, physical function and cognitive function in the cited literature

Measures and definitions	Differences in operationalization
Multimorbidity
(1) Disease counts Number of diseases on a continuous scale or categorized in accordance with specific cut-offs (2) Patterns of diseases Systematic associations amongst diseases defined on the basis of expert criteria or statistical associations (3) Weighted indices Scores derived from disease weights obtained for specific outcomes (e.g. Charlson, CIRS) (4) Speed of disease accumulation Rate of change in the number of diseases in a given observation period (5) Comorbidities of an index disease Combinations of diseases that occur together with the index disorder	Diseases may include: • Chronic or acute and chronic conditions • Symptoms, syndromes and/or risk factors • Conditions selected from specific existing lists or on the basis of a priori criteria such as the prevalence or predictability of specific outcomes • Conditions that were self-reported, diagnosed by a physician or inferred from medication use
Impairment of physical function
(1) Mobility limitations Limitations in the ability to move around that may eventually impair a person’s ability to accomplish daily activities (2) Strength limitations Limitations in upper or lower limb muscle strength as defined by specific thresholds (3) Limitations in the activities of daily living (ADL) Number of activities that a person can only accomplish with the help of another person	• Mobility may be assessed with objective tests (e.g. usual walking speed) or via self- report (e.g. SF-36) Strength may be objectively measured or inferred from the self-reported ability to perform specific tasks • ADL may include personal ADL (PADL) and instrumental ADL (IADL), counted sepa rately or grouped in an overall score • Measures of mobility and strength may be embedded in a more comprehensive test (e.g. SPPB, frailty phenotype)
Impairment of cognitive function
(1) Dementia Loss of cognitive function that interferes with daily life and ADL (2) Cognitive impairment Difficulty with global cognitive function or specific domains of cognitive function (e.g. memory, decision-making, concentration, learning) that does not interfere with daily life and ADL (3) Cognitive decline Decline of global or specific domains of cognitive function over time	• Diagnosis of dementia may be based on neuropsychological assessment by direct clinical examination (e.g. NIA-AA, DSM) or derived from hospital registries • Dementia can be further classified by age of symptom onset (early/late onset), symptom severity (mild/moderate/severe) or demen tia subtype (vascular/mixed/Alzheimer’s/ secondary) • Cognitive impairment and decline may be assessed by face-to-face neuropsychological assessment, by telephone interview (e.g. TICS) or reported by the affected person or a proxy • Cognitive impairment and decline may be assessed with global cognitive measures (e.g. MMSE, MOCA, CDR, GDS) or domain specific tests (e.g. digit symbol test for evaluating attention)

ADL, activities of daily living; CDR, Clinical Dementia Rating; CIRS, Cumulative Illness Rating Scale; DSM, Diagnostic and Statistical Manual of Mental Disorders; GDS, Global Deterioration Scale; IADL, instrumental activities of daily living; MMSE, Mini-Mental State Examination; MOCA, Montreal Cognitive Assessment; NIA-AA, National Institute on Aging and Alzheimer’s Association; PADL, personal activities of daily living; SF-36, 36-Item Short Form Health Survey; SPBB, Short Physical Performance Battery; TICS, Telephone Interview for Cognitive Status.