Over the past 20 years, the rates of autism spectrum disorder have been steadily climbing in developing countries, with a reported 30 percent increase in the US in just two years. But scientists have struggled to work out what's behind this epidemic, and now a new study suggests that we may have been looking in the wrong places. In fact, the epidemic might not exist at all.

A study of more than one million children in Sweden has shown that, over the 10-year period from 1993 to 2002, the number of autism spectrum disorder diagnoses increased significantly (just like it did in the US), but the number of patients who actually displayed symptoms remained stable.

This suggests that, rather than being in the middle of an 'autism epidemic', there might be a range of factors that are simply causing us to diagnose the disorder more often - something that's previously been suggested, but has been hard to test.

To investigate further, researchers from the University of Gothenburg in Sweden looked at two datasets - one that involved a comprehensive study of nearly 20,000 twins, and one that involved more than one million children, all born in Sweden between 1993 and 2002.

They then contacted the parents to find out whether their children showed any symptoms associated with autism. The researchers found that, surprisingly, the number of children who met the criteria for having an autism spectrum disorder remained the same over the 10-year study period. Despite the fact that the official prevalence of children diagnosed with autism had gone up.

After lengthy analysis of the data, the researchers published their findings in the new issue of the British Medical Journal. The results suggest that it's administrative changes, not an increase in the prevalence of the condition, that's pushing diagnoses up. Earlier this year, a Danish study came to a similar conclusion, suggesting that almost two-thirds of the increase in autism diagnoses in Denmark were due to the way the disorder is diagnosed and monitored.

If scientists hadn't already put to bed the myth that vaccines and autism are linked, this new research could help put the nail in the coffin.

However, we may already have taken a promising step towards reducing over-inflated autism rates. At the start of last year, the diagnostic criteria changed, and it's predicted that diagnoses may drop as a result.

While the Swedish researchers are convinced that the prevalence of autism spectrum disorders isn't on the rise, they also think we shouldn't waste too much time and money trying to figure out what was causing the perceived epidemic.

"The research and clinical resources currently devoted to dealing with these problems relate to the possibly mistaken notion that there is an actual increase," they write in the British Medical Journal

Instead, they say that funds would be better spent helping to treat people who have a range of intellectual or developmental disabilities. As Russell Saunders reports for The Daily Beast: "However symptoms are classified and defined, it will be no less important for those with special needs to get the services to help them."

Hopefully this new research won't take anything away from those with autism spectrum disorder, but will allow doctors and researchers to focus more time and energy working with those who need a little extra support.