Altered diagnosis has led to growth in autism

In Denmark, at least, study reported in 2014 says that the spike in the number of autism cases has to do with the way it’s diagnosed and an overall increased awareness of the disorder itself.

Just how that statistic relates to the US and the rest of the world, though, remains to be seen.

blocks showing a bar chart rise

Explaining the rise in autism cases?

A new study from Aarhus University, for the first time, confirms a widespread hypothesis: More than half of the increase in the Danish autism statistics can be explained by changes in the way diagnosis are made and cases registered. nly forty percent of the notable increase in autism cases that has been registered during the past few decades were due to causes that are as yet unknown.

Autism spectrum disorders are considered to be among the most serious child psychiatric disorders. The researchers state that the majority of the increase – a total of 60 percent – can now be explained by two combined factors: changes in the diagnostic criteria and in the registration to the national health registers.

The autism study

By studying disease prevalence among all individuals born in Denmark in the period 1980-1991 — a total of 677,915 individuals — researchers were, for the first time, able to confirm a widespread hypothesis, which is that an altered focus on autism can directly explain the majority of the dramatic increase in the disorder’s statistics.

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“What our study shows is that you cannot really talk about an autism epidemic, even though Denmark and other countries are currently experiencing a dramatic increase in the number of cases of autism spectrum disorders. We can see that a large part of the explanation lies in the huge changes in the area of diagnosis and registration which took place in the middle of the 1990s,” says PhD student Stefan Nygaard Hansen from Aarhus University.

The results were published in the medical journal JAMA Pediatrics.

Focus on two changes

The researchers have specifically focused on a change in the diagnostic system used by psychiatrists. This change occurred in 1994 and meant that autism is today recognized as a whole spectrum of disorders. But it also included an alteration in the specific symptoms that form the basis of the autism diagnosis.

The other important change took place in 1995 when the Danish national health registers began to include diagnoses made in connection with outpatient consultations. Before then, only diagnoses from hospital admissions were recorded. Both changes have thus occurred after the period in which the persons incorporated in the study were born. This has made it possible to compare the number of diagnoses made before and after the alterations within the same birth cohorts.



The study shows that the change in the diagnosis system in 1994 has affected boys considerably more than girls, but that the inclusion of outpatient diagnoses in 1995 has affected both genders equally.

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“Putting it simply, we can say that a person with an autism diagnosis has a slightly different symptom profile after the middle of the 1990s than previously, which is reflected in the statistics,” says Stefan Nygaard Hansen.

“But even though we have now shown that a large part of the increase among the Danish population is due to changes in diagnostic and registration systems, it is still important to point to the 40 percent of the increase which we cannot explain. We therefore need to continue to look for the factors which can explain this,” says Professor Erik Parner, Aarhus University.



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