(USA Today) - A new study of health records from California suggests that rates of attention deficit hyperactivity disorder (ADHD) have jumped by 24% since 2001.
"That is a very significant increase," says Darios Getahun, a research scientist with the Kaiser Permanente Southern California Medical Group who conducted the study.
The apparent rise in diagnoses is likely caused by growing awareness of the condition among parents and doctors, he and other specialists say.
The study looked at health records of more than 840,000 children, ages 5-11, who met a strict definition for ADHD, as diagnosed by a trained expert. It found that 2.5% of children were diagnosed with ADHD at the start of the study in 2001, vs. 3.1% in 2010.
The percentage diagnosed is lower than in many other studies because of the strict diagnostic criteria and because, unlike other research, the study relied only on health records, not parents' reports, Getahun says.
The study, published in Monday's issue of JAMA Pediatrics, was also large enough to break down those diagnosed by gender, race, family income and age. It found that boys were three times more likely to be diagnosed than girls. That may suggest that boys are more vulnerable to ADHD, as they are to autism, Getahun says.
It also may be because girls with the condition are often overlooked, says pediatrician Craig Garfield of Northwestern University's Feinberg School of Medicine and Lurie Children's Hospital of Chicago. "We know that girls are more likely to show signs of inattention as opposed to hyperactivity, and therefore, the disorder often goes unnoticed and untreated."
The study also found that the gender gap is closing among black Americans, with a lot of the increase over the past decade explained by a rise in diagnoses among black girls.
Children of higher-income families are more likely to be diagnosed with ADHD, Getahun says, perhaps because their families are more concerned with their school performance and are more likely to seek a diagnosis.
Several ADHD experts question the validity of the study and whether the apparent increase in ADHD should be cause for concern.
"I don't agree with the language about 'epidemic' proportions and 'dramatic' increases," says Paul Hammerness, an ADHD expert at Harvard Medical School and Massachusetts General Hospital. "It is my impression that absolute rates are fairly stable over time, from country to country as well."
Instead of worrying about an increase, Hammerness says Americans should focus on the quality of care provided to children with ADHD.
Benjamin Lahey, a psychologist at the University of Chicago, also questioned the study's methods and validity.
"I'm concerned that this paper will raise concerns that are not justified," says Lahey, who was on a scientific panel in the 1990s that helped develop the current definition of ADHD. "It certainly should not lead to the conclusion that there's an increase in the prevalence of ADHD in the United States."
The only thing the study shows is that diagnoses are rising among members of Kaiser Permanente health plans, he says. That may be because Kaiser Permanente under-diagnosed ADHD before or is over-diagnosing it now, he says — though he adds that he believes the former is more likely.
The study's reliance on doctors' records is also a weakness, he says. Doctors are notoriously inconsistent in how they diagnose ADHD, Lahey says. The same doctor is likely to judge two children very differently and may even give a different diagnosis to the same child seen on different days. The only way to do a reliable study, he says, is to use a specialized rating scale and consistent interviews scaled independently. Such research is very expensive and unlikely to be done, he adds.