More children are being diagnosed with attention deficit hyperactivity disorder (ADHD) now than were a decade ago, according to new research from a large California health plan.

It's not clear what's behind that trend, researchers noted. Possible explanations include better awareness of the condition among parents and doctors or improved access to health care for kids with symptoms, according to Dr. Darios Getahun, the study's lead author.

Prior research has also shown an increasing trend in ADHD diagnoses, according to Getahun, from the Kaiser Permanente Southern California Medical Group in Pasadena.

However, his team had strict criteria for determining which kids had ADHD, requiring a clinical diagnosis and prescriptions for ADHD medications. Past studies have relied on parent and teacher reports alone, Getahun noted.

In an analysis of Kaiser Permanente medical records, researchers found the proportion of five- to 11-year-olds diagnosed with ADHD increased from 2.5 percent in 2001 to 3.1 percent in 2010.

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