BACKGROUND
Multimorbidity is the coexistence of two or more long-term conditions. Patients with multiple conditions are common and have poor outcomes, including decreased quality of life, longer hospital stays, and higher costs of care.1,2 Models have been proposed to support clinical intervention in multimorbidity,3–5 but they are limited in scope and practical application. This paper offers a broader theoretical framework within which multimorbidity can be explored, from three perspectives:
the clinical encounter — the consultation between practitioner and patient;
service delivery — with increasing demands on limited healthcare resources, there is a need to deliver services more effectively and efficiently; and
clinical governance — measures of clinical quality are becoming increasingly relevant.
CONSTRUCTS OF THE MODEL
The model takes as its starting point the systems approach of Kurtz and Snowden.6 Three domains are proposed:
ordered (simple or complicated), where there is a simple relationship between cause and effect that can be understood by analysis of its component parts;
transitional, with features of both ordered and unordered systems; and
unordered (complex or chaotic), in which there is no simple relationship between cause and effect. The system cannot be understood by a reduction into its parts, although patterns emerge from the underlying interactions, and causality may be inferred retrospectively. Chaotic is used in the sense of unstructured randomness with no relationship between cause and effect, rather than the mathematical chaos, which is deterministic.
The structure of each domain has implications for clinical decision making and health service delivery, illustrated by a case study of morbidity (Table 1).
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The ordered domain
Simple ordered
There is a single-ordered clinical problem and a predictable and linear relationship between cause and effect. Small inputs give rise to small outputs and vice versa. Outcomes are well defined and …