The population rate of any particular ‘under-‘ or ‘over-testing, diagnosing or treating’ relates to only one of the multiple considerations that are likely to be important to the individual. While it may be a very important one (e.g. cause-specific mortality), addressing it as a specific consideration in a clinical encounter may undermine the possibility of establishing the optimal action for this person in their multi-criterial health portfolio. At the individual level there can only be ‘mis-‘, not ‘over-‘ or ‘under-‘, where ‘mis-‘ is defined in relation to the personally optimal action – a concept given increased legal relevance in the UK as a result of the recent Montgomery ruling on informed consent.

A Multi-Criteria Decision Analysis (MCDA)-based decision support tool can assist the person in determining the optimal course of action and avoid the possibility of any ‘mis-‘. The structure of such a tool comprises the available options and person-relevant criteria. The cells in the resulting matrix are filled with the performance rates of each option on each criterion and these are combined with the person’s criterion importance weights to produce an opinion in the form of the full set of rated options. Importantly, no ‘over-‘ or ‘under –‘ possibility features as a criterion since the performance ratings must reflect the best estimates available nowfor the potential benefits and harms resulting from each option. These will normally be on scales and the scale values used must be the absolute ones, not ones that have already undergone (necessarily value-based) segmentation. Applying guideline-based cut-offs, based on population-level value judgements, to establish ‘risk classifications’ and hence a recommended action, is incompatible with truly preference-sensitive person-centred care.

Following the production of a number of MCDA-based decision support tools, the weight management tool currently under development includes a variety of Nutritional, Activity, Behavioural, Cognitive, Pharmacological, Endoscopic and Surgical therapy options. In the basic case, the criteria for individuals to weight comprise both the potential benefits (Effects on Life Expectancy and Health Related Quality of Life) and harms (Side Effects/Adverse Events, and Treatment Burden). Various scales are being drawn on to produce the required performance rates, but use of many is hampered by their dependence on BMI-based segmentation and definitions of overweight and obesity. As has been pointed out elsewhere, ‘evidence-based person-centred care’ is an oxymoron unless ‘evidence-base’ is re-interpreted simply as the underlying data, not accompanied by pre-emptive option evaluations, especially ones resulting from the use of thresholds.

A preference-sensitive MCDA-based support tool will often produce an opinion for an individual that is out of line with mono-criterial threshold-based guidelines, confirming that ‘mis-‘, not ‘over-‘ or ‘under-‘ testing, diagnosis and treating is the relevant issue to be addressed in moving to person-centred care. Arguments about what threshold/s should be used, should be abandoned and absolute values used in clinical decision-making. To facilitate this, researchers should publish and analyse scale data at maximum practical granularity, without the threshold partitioning that may facilitate robust scientific analysis, but can interfere with the delivery of individualised care.