A sub-study of Autism Spectrum Disorders (ASD) headed by Ms Posserud was conducted as part of the "Barn i Bergen" (Children in Bergen) project. The study shows that the diagnosis of ASD may apply to as much as one per cent of the population.

ASD is a collective term for diagnoses such as autism (childhood autism), Asperger's syndrome, atypical autism and other autistic traits. The classic signs of autistic behaviour include communication difficulties, poor social skills, repetitive behaviour and narrowly focused interests.

Different results

A study conducted in 1998 found that autism occurred in 0.05 per cent of Norwegian children. The figures from the "Barn i Bergen" project could therefore be interpreted to mean that the incidence of autism has risen dramatically. However, Ms Posserud thinks it is important to downplay the difference in results.

"It is difficult to know whether the differences in these studies reflect a genuine increase in the incidence of ASD. Our conclusion is that the rise in ASD can be explained mainly by the use of more thorough mapping methods and, consequently, that we are not seeing the emergence of an autism epidemic," says Ms Posserud, who is a doctor and researcher in the field of child psychiatry at Haukeland University Hospital in Bergen.

Broader diagnosis

Researchers involved in the "Barn i Bergen" project got widely varying results when they used different methods to investigate the same group of children. The first sub-study concluded that 0.44 per cent of the children had ASD, whereas the result a few years later was 0.87 per cent.

According to Ms Posserud, the reason for the difference is that the researchers conducted a more extensive survey in the last sub-study, which included a comprehensive clinical test in addition to a questionnaire and interviews with the children's parents.

"The clinical test revealed several additional cases of the disorder. This suggests that a diagnosis of ASD cannot be ruled out merely on the basis of interviews with the parents," Ms Posserud explains.

According to Ms Posserud, it is the children with normal intelligence who most often go unnoticed. These children were not included in the definition of autism a few decades ago when the diagnosis was only applied in the most serious cases. Today ASD covers difficulties with social interaction across a range of intellectual abilities. Since the definition has been expanded, many more people have been diagnosed with autism.

The research was funded by the Research Council's Programme on Mental Health (PSYKISK) in Norway.