Receiving a diagnosis of a learning disability can be crucial for an individual, and screening tools can help to achieve this, as Dr Karen McKenzie explains:
There are several stages where an individual might be identified as being likely to have a learning disability. For example, at birth if the baby has a syndrome that results in, or is associated with learning disability; at school where the child’s progress may be at odds with their peers; or on transition from childhood to adulthood where most young adults become increasingly independent and undertake work or further education.
At each stage, receiving a diagnosis of learning disability can bring significant benefits. This includes explaining some of the child’s difficulties; ensuring that they receive appropriate support throughout his/her development; provision of relevant information, and access to welfare benefits and specialist services if required.
Unfortunately, many individuals do not have their learning disability recognised, or diagnosis is delayed and, as a result, do not receive any additional formal support, which can result in their being disadvantaged in many areas of their life.
One significant area may be health provision. It has long been established that many people with a learning disability have complex and multiple healthcare needs that may be unrecognised, unmet or inadequately addressed (NHS Health Scotland, 2004). While the introduction of routine health checks for people with a learning disability has gone some way to address this (Robertson et al, 2010) it relies on GPs being able to identify who on their caseload has a learning disability in the first place. This has historically been a difficult task, particularly as healthcare professionals may have limited knowledge about what a learning disability is (McKenzie et al, 2000).
Providing appropriate support to access healthcare is as important in acute care settings as in primary care settings. While there are an increasing number of liaison nurse schemes, where specialist learning disability nurses provide support to service users in hospital settings, again this relies on the individual being diagnosed in the first place.
Failure to identify that someone has a learning disability and to provide support tailored to their needs may also have consequences in areas such as housing and relationships. Research suggests that homeless people are significantly more likely to have a learning disability (Oakes and Davies, 2008). Similarly, parents with a learning disability are considerably more likely to have their children removed from them, although research suggests that many can improve their parenting skills if given appropriate support (Booth et al, 2005).
There is also increasing recognition that a significant number of people are being caught up in the criminal justice system where their learning disability may be unrecognised. As a result, they are likely to be vulnerable to exploitation, bullying, and are at risk of being disadvantaged and unsupported at various stages of the criminal justice process (eg. Talbot, 2008; 2010).
In summary, being identified as having a learning disability is crucial to ensure that an individual has appropriate support at all stages of his/her development. Failure to do this and, by extension, access support, can result in a range of detrimental consequences for the person throughout their lives. Unfortunately, many people with a learning disability continue to go undiagnosed.
Diagnosing a learning disability
There are a number of reasons why someone may not be diagnosed. Diagnosis requires the person to meet three criteria: a major impairment in intellectual disability (an IQ of 69 or less); major impairment in adaptive functioning, such as in areas of self-care, safety or relationships; and childhood onset (British Psychological Society (BPS), 2001). This requires assessment in all of these areas. The assessment of intellectual functioning must be carried out by a qualified applied psychologist, on an individual basis, using a properly standardised test that has good psychometric properties (BPS, 2001).
The increasing restriction of budgets may mean that learning disability services could be reluctant to provide support until the person has been diagnosed. This, coupled with a limited number of psychologists, may result in the psychologist being forced into an unwelcome gatekeeping role and a bottleneck could form while individuals wait for diagnostic assessment before being able to access services.
This problem could be exacerbated because people may be referred to learning disability services that do not have one. This could be for a number of reasons including low levels of knowledge about what a learning disability is (McKenzie et al, 2000; Rae et al, 2011); confusion between the terms ‘learning disability’ and ‘learning difficulty’ with the latter referring in the UK to specific rather than global cognitive difficulties, such as dyslexia; and that educational services and legislation may not commonly use the term ‘learning disability’ to describe the needs of children (eg. Scottish Executive, 2004). This can mean that many people who clearly would not meet the criteria for having a learning disability may be referred for assessment, adding to the demands on diagnostic services.
In addition, in many settings where there is an urgent need to identify whether someone has a learning disability or not, such as police stations, courts, prisons and accident and emergency departments, access to a psychologist is likely to be limited or lacking.
Screening tools
The challenges to quick and accessible diagnostic assessment have led to increasing interest in the use of screening tools in a range of settings. Professional bodies, such as the BPS, have recognised that screening tools can offer a practical solution where services are unable to meet demand for diagnostic assessment in a timely way (BPS, 2003). While it cannot replace full diagnostic assessment, a good screening tool can offer an accurate indication of whether an individual is likely to have a learning disability or not.
What makes a good screening tool?
There are a number of properties that need to be taken into account when designing a good screening tool, the majority of which are applicable to the development of any robust psychometric assessment (Terwee et al, 2007), with others being more specific to screening tools (eg. Glascoe, 2005).
Firstly, the screening tool must be valid, meaning it should measure what it is meant to measure – in this case whether a person has a learning disability or not. As mentioned earlier, being considered to have a learning disability can have significant consequences for an individual. Therefore it is important that screening tools are as robust as possible and minimise misidentification.
One key way of determining how good a screening tool is is to measure its sensitivity and specificity (eg. Glascoe, 2005). Sensitivity is the extent to which it correctly identifies those who do have a learning disability, while specificity relates to how many it correctly identifies who don’t, at a given cut-off point on the tool. These are usually reported as percentage scores, with 70% and above being commonly taken as acceptable for sensitivity and 80% and above for specificity (Glascoe, 2005).
A good screening tool is also expected to correlate well with the two criteria for learning disability of impairments in intellectual and adaptive functioning. As such, the higher the IQ or adaptive functioning score, the higher the screening score should be and vice versa, indicating convergent validity. It might also be expected that those with a learning disability would have a significantly lower score on the screening tool (assuming that a higher score equalled better adaptive and intellectual functioning) than those without, indicating that it achieved an aspect of discriminative validity.
Further important properties of a screening tool are that it is quick and easy to use, and gives consistent results when conducted in a range of settings by different people with varied backgrounds and levels of knowledge and experience. This latter property can be measured by inter-rater reliability; ie. the extent to which two independent people agree when screening the same person. If using the tool results in a lot of disagreement it suggests that it may not be accurate. It is also important that a screening tool gives stable results over time. This can be examined by test-retest reliability, which looks at the agreement of the results of an assessment when administered on two separate occasions over time.
Examples of screening tools in practice: The LDSQ and the CAIDS-Q
While some services use screening tools, research suggests that many are developed locally, have no or only a limited evidence base, and have not been tested in terms of their psychometric properties (eg. Talbot, 2010). In this context, two evidence-based screening tools are presented: one for adults aged 16 upwards, the Learning Disability Screening Questionnaire (LDSQ: McKenzie and Paxton, 2006) and the other for children aged eight to 18, the Child and Adolescent Intellectual Disability Screening Questionnaire (CAIDS-Q: McKenzie et al, 2012).
Both are short – consisting of seven items – and are quick and easy to use. They do not require the user to have particular training, qualifications or professional background and can be completed directly with the individual thought to have a learning disability or someone who knows him/her well. Both assessments have been found to have strong psychometric properties demonstrating good inter-rater reliability and discriminative and convergent validity.
Importantly, both show good sensitivity and specificity, with the LDSQ identifying those with and without a learning disability with 91% and 87% accuracy respectively (McKenzie and Paxton, 2006) and the CAIDS-Q having equivalent figures of 97% sensitivity and 86–87% specificity, depending on the age range being examined (McKenzie et al, 2012).
The screening tools are widely used in a range of services across the UK and abroad and have been recommended for use in criminal justice systems in England and Wales, following a pilot study by the Department of Health. They may also prove useful for researchers who require a quick, easy and accurate means of determining who is likely to have a learning disability for research purposes.
Screening tools such as the CAIDS-Q and LDSQ can also help:
• Education services to identify children who may require additional support, or as part of the transition process
• Midwives, child protection staff and health visitors to identify parents who are likely to have a learning disability
• Accident and emergency department staff to know which individuals may require learning disability nursing liaison support
• Health staff in adult mental health and other specialist services to identify those who may also need support from learning disability services.
If used well, with an awareness of their limitations, screening tools can offer ways of improving the journey of people with a learning disability through a range of statutory and non-statutory systems.
Limitations
But screening tools have limitations. It is as important that screening tools have a strong evidence base, good psychometric properties and are fit for purpose as full intellectual and adaptive assessments used for diagnosing a learning disability.
There are significant dangers of using inappropriate screening tools, or ones that have no evidence of their psychometric properties, were not designed to be used as such or are adapted from established tools. Even omitting one item from a validated screening tool can have a significant impact on its accuracy, and choosing particular items, without carrying out research to see how accurate they are in terms of sensitivity or specificity, may potentially be no better than allocating people randomly to categories in terms of whether they have a learning disability or not. It should also be remembered that even the best screening tool is still just that and cannot replace a full diagnostic assessment.
Conclusion
Having an unrecognised learning disability may be detrimental in many spheres of life. Screening tools that are valid and reliable offer a pragmatic alternative in situations where diagnostic services are limited or lacking, however it can never be a replacement for diagnosis.
About the author
Dr Karen McKenzie is senior lecturer/chartered clinical psychologist at the University of Edinburgh.
References
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