Skepticism about the 2011 Korean Study

In The Politics of Autism, I discuss the uncertainty surrounding estimates of autism prevalance.  Jessica Wright reports at SFARI:

A widely cited 2011 study that pegged autism prevalence in South Korea at a whopping 2.6 percent is inherently flawed because of the assumptions the researchers had to make, suggests a new analysis of the data1. The findings have implications for estimates of autism prevalence anywhere in the world.

Intense controversy surrounds estimates of autism prevalence, which have been rising steadily over the past 30 years. How researchers collect their data can have a huge impact on the numbers, and may even account for the rapidly rising rates.

The 2011 study garnered attention for its two-phase design, in which researchers screened more than 20,000 children for autism and then clinically assessed a small proportion2. They extrapolated these findings to South Korea’s population to arrive at their estimate.

Three-quarters of the children the study tagged as having autism did not have a prior diagnosis and were attending mainstream schools. Flagging children based on signs noted in medical and school records — the standard method in the U.S. — may have missed these children.

But the two-stage design is also flawed. The screening method the researchers used is not perfectly accurate, and the results can be skewed by which parents choose to participate. Taking these limitations into account, the analysis, published 29 June in Autism, says the 2011 study’s range for autism prevalence could have been at least 2 to 5.4 percent.

This numerical spread is too wide to allow researchers to pinpoint any single rate with certainty, says lead researcher Dan Kennedy, assistant professor of psychological and brain sciences at Indiana University in Bloomington.

“The estimate can be misleading if incorrect assumptions are made,” Kennedy says. “If we are overconfident in the assumptions we make, then we end up with an estimate we believe, but probably shouldn’t.”