Increased diagnosis of developmental disorders: Are there really more children with Autism, Dyslexia, or ADHD?

Studies have shown that the number of children diagnosed with childhood developmental disorders, which include dyslexia, autism spectrum disorders, and attention deficit hyperactivity disorders (ADHD) has risen sharply in the western world over the last twenty years.

Most experts, clinicians and epidemiologists, largely attribute this to changes in diagnosis rates and greater awareness of the conditions. They argue that the number of children with symptoms of these conditions has remained largely stable, it is just that more children are identified and diagnosed today than ever before. This is due to shifts in diagnostic criteria so that more children are included in the categories, and the changing cultural context which emphasises differences.

On the other hand, many lay people affected by, caring for, or working with children with developmental disorders, and some researchers, believe that such explanations may not tell the whole story. They have argued that the rising prevalence may reflect a real increase in the number of children with difficulties symptomatic of the disorders. Many have suggested that rising prevalence could be underpinned by changes in environmental causal factors.

Our analysis will examine whether increases in the numbers of children diagnosed have been accompanied by increases in behaviours and impairments symptomatic of these conditions, or whether symptom levels have remained constant with diagnosis increasing, (so the labels are simply applied to more children).

All three conditions are relevant because all are classed as developmental disorders, with debate over the boundaries of the disorder, and even the existence of a "disorder" at all. The children in our studies will be from the Avon Longitudinal Study of Parents and Children, (ALSPAC), where children were born in 1990 or 1991, and the Millennium Cohort Study (MCS), where the children were born ten years later, in 2000 or 2001.

As we expect, there are far more children diagnosed autism and ADHD in the later MCS study. Data from these two studies will allow us to compare the number of seven year old children with symptoms of each disorder in 1998 to the number with symptoms in 2007. This will show whether the rises in diagnosis are reflected by a rise in number of children with underlying symptoms. Crucially, both studies have recorded similar diagnostic, cognitive and behavioural measures, making a direct comparison possible. It is important to determine whether there is an underlying increase in symptoms, because if so, environmental or social factors are probably responsible and could become targets for intervention and or prevention.

Boys are more likely than girls to suffer from autism, dyslexia and ADHD. But if girls and boys are suffering from an equal level of difficulties (the same symptom levels) our previous work suggests that the boys' difficulties are more likely to be recognised than the girls'. Are boys are more likely to be diagnosed, even when girls we compare them to have similar levels of symptoms? Our second aim is to establish whether boys are more likely than girls to receive an ASD or ADHD diagnosis, or be identified as dyslexic, regardless of symptom levels. This should provide clinicians and educators with important information about which children are missing out on services designed to help them.

Our final aim is to explore overlap in symptoms between the conditions. Much research suggests that some children share symptoms of autism, dyslexia and ADHD. This had led scholars to question the diagnostic criteria for developmental disorders in their current configuration. We will look at which disorders children with co-occuring symptoms are likely to be labelled with. This is extremely important because the diagnostic label may determine the interventions children receive.



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The beneficiaries of the research reflect the interdisciplinary nature of this collaboration:

1) Epidemiologists, social scientists

2) Clinicians and educational psychologists

3) Health policy makers, such as those involved in diagnostic guidelines (e.g. American Psychiatric Association, World Health Organisation; Research funding bodies (e.g. NIHR, MRC, ESRC); educational psychology bodies issuing guidelines (e.g. the British Psychological Society).

4) ADHD and ASD charities and support groups, parents, relatives, affected adults and children.

How will they benefit from this research?
The proposed work will contribute to the evidence base that informs epidemiologists about the nature of potential underlying causes of diagnosis of autism, ADHD and dyslexia. If symptom levels are increasing over the study period, explanatory risk factors that have changed in the recent past, be they social, environmental, gene/environmental, family-based or educational factors, are potential targets for intervention and or prevention and are therefore important to identify. It will also inform sociologists about the extent to which symptomatic behaviours of ASD and ADHD have become medicalised (under the medical domain) over the recent past.

For clinicians and educational psychologists, findings will highlight characteristics such as gender and cognitive ability that influence which groups of children are more likely to be bought to the clinic, informing them about which children slip through diagnostic nets, and why. This research will expose the influence of gender, cognitive ability and social factors on diagnostic practices, as opposed to direct diagnosis by symptoms of each condition.

Overlap in symptoms between conditions will benefit bodies that set diagnostic criteria such as the American Psychiatric Association and World Health Organisation as they examine the validity of current diagnostic categories. Research funding bodies (e.g. National Institute of Health Research, NIHR) will be informed about whether funding the search for underlying environmental causal factors of these disorders should be prioritised. Our findings, particularly concerning dyslexia will also be of interest to educational psychology bodies issuing guidelines (e.g. the British Psychological Society), because they will shed light on how their current definition of dyxlexia (which does not require a discrepancy between IQ and reading ability) are currently implemented. This has consequences for which children are classified as dyslexic. All of the above institutions will be targeted through 2-page policy briefs, issued through the ESRC Centre for Genomics in Society, where the PI will be based for 40% of her time.

The project will provide information for parents and affected individuals too, improving understandings of ASD, ADHD or dyslexia diagnosis in terms of their historical context. According to parents that have taken part in previous studies, it will also help them assess the merits of diagnosis and meet their need for broad information when assessing recommendations of educators and clinicians. Parents, and parent-led charities will directly benefit because they will be better informed about links between diagnosis and symptoms for children. This has been a major source of debate and mobilisation of parent groups and the findings will be communicated to these actors through targeted press releases again referring to academic publications that result.