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Five common mistakes made by Mental Capacity Assessors

Updated: Sep 22


In my experience as quality monitoring team leader, having reviewed and supported over 500 mental capacity assessments for many different decisions (ranging from health and welfare and financial decisions around testamentary or litigation capacity), I’ve seen patterns and commonality in what we, as assessors, often miss.


Here are mistakes I want to draw attention to:

  • Check which legal test is correct for the decision in question – often, our immediate assumption is that the decision will be assessed under the Mental Capacity Act (2005), but this is not always the case. For instance, if we are assessing a patient’s capacity to be able to use social media and the internet, this would be assessed under the Re A (2019), or a patient’s capacity to decide who to be in contact with, this would be under Re B (2019) rather than the MCA.

Whether it’s the MCA’s two-stage test or case law, this will determine where the threshold of understanding is set and, therefore, could quite significantly change the goal post for what the patient needs to know. Ultimately, this might be the difference between them having or not having capacity.

  • Consider how you have attempted to support the individual during the assessment – this might seem like an obvious one, given it is the second principle of the MCA – but in my experience, this will often be one of the first things to be overlooked, particularly when the practitioner is under pressure to rush the assessment or get it all done in one session.

Give yourself time to consider what you are bringing to the assessment, and does this meet the patient’s needs? What supportive materials are you using? where are you holding the assessment? and can anyone be used to support the patient?

  • Think about how you are assessing their understanding, retention and weighing-up of the relevant information. Again, obvious right, but in the moment, it’s a common mistake and only when an assessor is writing up their assessment does it become apparent that not enough questions were asked to explore how the patient assimilated any new information.

It’s not enough to give the patient the information and then ask if they understand this - you have to ask further question to investigate how they have interpreted what you said to them, how this has fitted in their own schemes and what questions or considerations it has brought up for them. So, find out what they think about what they have heard / been told and is there a congruency between the two?

  • Consider whether the patient has given you information that needs corroborating before you reach your conclusion. Often, when this hasn’t been done, it’s because of time pressures on the health practitioner i.e. not having the luxury of time post-assessment to find the right person to ask, or new information coming to light that then requires follow up questions for the patient, or the time pressures of the decision itself.

So, my advice would be to identify who could be good sources of information before beginning the assessment and gather as much information as possible. Then you can validate as you go through the assessment and challenge (where appropriate) the information or scenarios given by the patient that differ from the accounts you already have.

This will also enable you to build up a more accurate question set based on the facts and allow you to explore these matters more fully in the assessment. If it must be done post- assessment, then consider it a necessary step rather than a desirable one as it could tip the balance one way or another of how the evidence stacks up.


It’s important to note that underpinning all of this is identifying accurate/trustworthy sources to corroborate against, so always think about the potential bias or subjectivity of these sources before taking it as fact.

  • Do not forget the causative nexus – this is often the overlooked stage of the assessment but is crucial to completing a robust assessment. Under the MCA, it’s not sufficient to simply evidence that there is an impairment or disturbance to the functioning of the mind or brain and that there is a functional inability – you must make a direct link between the cognitive impairment directly causing the lack of understanding/retention/ability to wight-up and use or communicate the decision in question.

Sometimes this link will be obvious but, in more cases than you might think, it’s not. For example, a diagnosis of schizophrenia or mixed dementia does not mean a lack of capacity without evidence of how it is impairing the patient’s ability to make the decision in question – a difficulty in retaining the relevant information in isolation does not mean a lack of capacity.


The patient’s impairment might impact much of their behaviour and may impact some of their decision making, but not all. So, before you conclude there is a lack of capacity, make sure you have established a clear and direct relationship between both stages of the two-stage test. If a causative nexus has not been established, then you have not met the requirements for a lack of capacity.


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