Functional abilities encompass a number of life domains and there is no definitive subset of abilities under the umbrella of functional status nor a ‘gold standard’ defining functional independence or dependence. As a result, dozens of measures of functioning exist that cover different life domains, with varying theoretical bases and psychometric properties. Recent initiatives, such as the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS)⁴ (sponsored by the National Institute of Mental Health) have attempted to rectify the heterogeneity of functional measurement approaches by validating and recommending a core set of functional assessments. Other NIH initiatives, such as the Patient Reported Outcomes Measurement Information System (PROMIS)⁵, are also underway to provide a standard ‘toolbox’ with which researchers and clinicians can select standardized population-normed instruments to measure functioning with self-report measures.

While the process of identifying a ‘core’ set of functional measures is ongoing, several important dimensions must be considered in any approach. The conceptualization of functional impairments generally separates what an individual can do (capacity) from what an individual does do (actual performance). Functional capacity refers to the ability of an individual to perform a task under optimal conditions and that performance can be measured with the observational or performance-based approaches described in the latter portion of this chapter. Actual performance may be discrepant from functional capacity, as real-world performance is affected by motivation, opportunities and environmental barriers.

In addition to the distinction between capacity and actual performance, the functional consequences of an illness can be judged in a number of ways. Functional status can be assessed relative to age-adjusted norms, premorbid ability or a criterion devised by an external entity (e.g. some government agency standard). The normative basis for assessing functioning is important when interpreting scores from instruments that are generic (e.g. the Medical Outcomes Study – Short Form) and meant to be applicable to the broad population. Alternatively, functioning measures can be disease-specific, such as those focusing on severe mental illnesses (e.g. the Independent Living Skills Survey). Although these latter measures may not provide an estimate of functioning relative to healthy older adults, the items may have a lower ‘floor’ and thus can guide rehabilitation targets in functionally impaired people.

Another way in which functioning can be classified, typically in population-based studies, are preference-weighted approaches. These approaches use population data on preferences for states of health to create indices of disability adjusted life years (DALYs) or quality adjusted life years (QALYs), which can be compared across illnesses or treatments. For example, the Quality of Well-Being Scale uses a preference-weighted approach. Previous use of this instrument estimates that the ‘well years’ lost to schizophrenia among middleaged and older adults are slightly more than that experienced by ambulatory individuals with AIDS⁶.

Yet another distinction in assessing functioning involves the source of the information. Not surprisingly, ratings of functioning provided by patients, their family members and their clinicians often show inconsistencies – for example, patients with depression may overestimate their impairment, while patients with diminished insight due to dementia may believe they are fully capable when they are not. Family and clinician judgements of functioning may depend upon the degree to which they are familiar with the individual’s functioning in the community. Some indicators of functioning, such as employment status or medication adherence, may be dependent on contextual factors such as availability of social support. Furthermore, daily living skills must be assumed to fluctuate within the individual, based both on the context and on the course of the psychiatric illness and its treatment, such that any point-in-time assessment of functioning may be biased by state-level factors (e.g. mood state, fatigue).

Taking all these considerations together, it is clear that attaining reliable and accurate representations of an individual’s level of functioning presents a challenge for clinicians and researchers. The best approach typically utilizes multiple measures of functioning (e.g. performance-based, subjective ratings) in different contexts (e.g. at home and in the clinic).

There is no single definition of daily life skills, but the primary functional categories include activities of daily living, social role functioning, decision-making capacity and recovery. The activities of daily living (ADLs) were defined in the 1960s and a decade later they were differentiated from instrumental activities of daily living (IADLs). ADLs include toileting, dressing, transferring and other activities basic to maintaining residence in the community. IADLs are more cognitively complex and involve fine motor movements, including managing medications, using the telephone, arranging transportation, managing money and preparing meals. In the general population, impairment in ADLs and IADLs increases with age, although the overall prevalence of ADL impairment in older people seems to have declined over the past several decades⁷. Change in ADLs often corresponds to change in disease status and not infrequently triggers placement in a care facility. Typically, ADLs and IADLs are rated by an observer or clinician, but self-perceived impairment in functional tasks is also frequently evaluated. Measures of perceived ability to complete functional tasks are embedded in subjective questionnaires (e.g. ‘Are you impaired in your ability to walk one mile?’) as well as whether a disease impacts functioning (e.g. ‘Has your mental health interfered with your social activities?’). Finally, a number of approaches to the measurement of general physical function are used to assess physical fitness in older adults (e.g. grip strength, sit to stand tests), but because these are not specifically tied to daily life skills, we will not describe them here. Interested readers are referred to an excellent review on these physical functioning instruments⁸.

Social functioning is another key domain in functional assessment. Actual performance can be measured in regard to an individual’s roles in the workplace, in close relationships and in leisure activities. In geriatric populations, particularly after retirement, social roles may be less culturally prescribed than among younger adults, which makes determining the extent of social impairment more challenging. Particularly in schizophrenia as opposed to mood disorders or dementia, social skills may be measured in standardized role-play tasks. These simulate conversations in which the participant’s performance is graded. The use of performance-based measures of social functioning is generally restricted to research.

Another context of functional status that clinicians are frequently asked to evaluate in older adults with mental health problems is decision-making capacity, particularly with regard to medical or other major life decisions. The assessment of capacity to make decisions should be specific to the context. For example, it cannot be assumed that impairment in the handling of personal finances signifies impairment in the making of medical decisions, such as the refusal of treatment. Assessing decisional capacity typically includes four components: understanding, appreciation, reasoning and expressing a choice. Understanding describes the extent to which the individual comprehends what is at stake, i.e. probable outcomes, risks and benefits. Appreciation measures how well the individual can relate the decision to his or her own situation, while reasoning measures the quality of the mental process by which the individual arrives at that decision. Finally, expressing a choice concerns whether the individual is capable and/or willing to express a decision. Research in older patients with schizophrenia or bipolar disorder using standardized measures of decisional capacity has indicated that cognitive impairments are the single greatest predictor of impairment in decisional capacity, over and above psychotic or affective symptoms. However, the manner in which the information is conveyed to the patient, particularly whether it is repeated, appears to make a significant difference in whether capacity is achieved. It cannot be assumed that the presence of a psychiatric disorder translates to a lack of capacity.

Finally, recent years have seen an emergence of a more patientcentred concept of functioning that is termed ‘recovery’. The precise definition of this term is debated, but a consensus panel formed by the US Substance Abuse and Mental Health Services Administration (SAMHSA) provided the following: ‘Mental Health recovery is a journey of healing and transformation enabling a person with a mental health problem to live a meaningful life in a community of his or her choice while striving to achieve his or her full potential’⁹. Although recovery shares a focus with the above domains on functional outcomes, greater emphasis is placed on the patient’s sense of self-efficacy and meaning. The measurement of recovery is thus more idiographic than that of the domains just described. How the construction of recovery changes, if at all, across the lifespan of people with mental illnesses has received little research.

Many factors influence functioning and daily living skills, including illness, cultural issues, environmental contexts and age-related changes. In this section, we review the impact of these factors and provide an integrative model that combines them.

Emerging evidence in a variety of psychiatric disorders suggests that cognitive impairments are the greatest contributors to diminished functional status^10,11. On average, the relative influence of cognitive impairments on functioning probably increases over the course of a long-term illness. This is in part due to declines in the acuity of psychopathological symptoms for people with early-onset mental illnesses¹²