As the ranks of kids diagnosed with ADHD in this country continue to swell—to 12% of school-age children and as many as 20% of teenage boys, according to the CDC’s latest count—it becomes more and more urgent to look at what forces might be driving this phenomenon.

The new CDC survey, in addition to measuring the nationwide prevalence of ADHD diagnoses, and how many children are being medicated for the disorder, gives us a tantalizing opportunity to compare figures across states and regions. And that gives us an opportunity to investigate the dramatic discrepancies that appear when you do.

For instance, a child in Kentucky is three times as likely to be diagnosed with ADHD as a child in Nevada. And a child in Louisiana is five times as likely to take medication for ADHD as a child in Nevada. Most of the states with the highest rates of diagnosis and prescriptions for medication are in the South, with some in the Midwest; most of the states with the lowest rates are in the West or Northeast. What accounts for this regional disparity? Stephen Hinshaw, a clinical psychologist, has been asking that question for nearly a decade, along with his colleague at the University of California, Berkeley, Richard Scheffler, a health economist.

What’s behind regional differences?

“We were looking for the ways in which the variation in diagnosis and treatment might be explainable on the basis of more than the particular child’s symptoms or the particular doctor’s office visit,” explains Dr. Hinshaw. “We thought it might have to do with the supply of providers—how many pediatricians or child psychiatrists in a given region—or the ways states supplement Medicaid. It might have to do with advertising. But it doesn’t take a genius to figure out that most kids first get noticed for ADHD in a classroom setting. So we wondered, are there policies about schooling that might be relevant?”

It turned out that there were indeed educational policies that vary from state to state that link to the rates of ADHD diagnosis.

Specifically, Drs. Hinshaw and Scheffler’s team found a correlation between the states with the highest rates of ADHD diagnosis and laws that penalize school districts when students fail. Some of these laws are what they call “consequential accountability statutes”—that is, laws like No Child Left Behind, which make school funding contingent on the number of students who pass standardized tests. Another kind of accountability law passed by many states requires exams for high school seniors to qualify for graduation.

When school funding is tied to test scores

“In 2001, No Child Left Behind put the whole country on notice that districts are accountable for scores,” Dr. Hinshaw notes. “But if you go back two decades earlier, in the early 1980s, some states got on the consequential assessment bandwagon earlier or the high school exam bandwagon earlier.”

What the team found is that in states that enacted these measures early, within a couple of years rates of ADHD diagnoses started going up, especially for kids near the poverty line. This isn’t surprising as the diagnosis helps the school comply in several different ways, Dr. Hinshaw notes. If kids who are struggling with ADHD get treated, it should improve their functioning in school and hence their test scores. But it’s also the case he adds, that in many jurisdictions, if you get an ADHD diagnosis your test scores don’t count. And, of course, there’s an added bonus that, since kids with untreated ADHD are often disruptive in the classroom, getting them to settle down (or sending them to segregated classrooms) could have positive impact on a whole class—and that class’s test scores.

In other words: When schools are given financial incentives to improve student success rates, students are more likely to be diagnosed with ADHD and given medication to treat it.

State-by-state differences in rate of diagnosis

To understand Hinshaw and Scheffler’s analysis, let’s take a step back and look at the numbers. The CDC has released a great tool that allows anyone to take a snapshot of what percentage of kids are getting diagnoses in individual states—as well as in each of 10 regions around the country—and what percentage are getting prescriptions for medications like Ritalin and Adderall.

The differences from state to state are stunning. For rates of ADHD diagnoses in children age 2-17, the spread runs all the way from Kentucky, which tops the list at 13.1%, to Nevada, at the bottom, with 3.8% diagnosed. That’s more than three times as many kids in Kentucky as in Nevada.

In terms of the percentage of kids who get ADHD medication, Louisiana tops the list at 9.2% and Nevada, again, comes in at the bottom, at 1.8%. That means Louisiana is more than five times as likely to medicate a child for ADHD as Nevada.

Differences by region

And the disparity isn’t just a matter of a couple of outlier states. The five states that have the highest rate of diagnoses—Kentucky, Arkansas, Louisiana, Indiana and North Carolina—are all over 10%. That’s more than twice the rate of the five states with the lowest percent diagnosed—Nevada, New Jersey, Colorado, Utah, and California, all at under 5%.

If you look at the rate at which children are medicated for ADHD, the same five states are at the top of the list, all of them with over 8% of kids getting medication. The states at the bottom of the list for medication—Nevada, Hawaii, California, Alaska and New Jersey—are all under 3.1%.

To take a look at where the states doing the most diagnosing and prescribing are, we note that the CDC divides the country into 10 regions. (You can see the map of the regions here.) The region that has the most ADHD diagnoses (9.3%) and the most kids on meds (6.6%) is the one that includes Kentucky, Tennessee, Georgia, Alabama, Mississippi, Florida, and the Carolinas (Region 4). For comparison, the region that has the least diagnoses (5.4%) and the least medication (3.1%) includes California, Nevada and Arizona (Region 9).

If we look a little more broadly, the four regions (4,6,7,5) that have the highest percentage of kids on ADHD medication (an average of 6.5%) are all grouped together, geographically, in the South and the Midwest. A slightly different group (4,5,6,3), but still across the South and Midwest, has the highest percentage of diagnoses (8.8% average).

The four regions (2,8,9,10) with the lowest percentage of kids diagnosed, all in the Northeast and West, have an average of 6% diagnosed, and the same four regions have the lowest rate of kids getting medication, 3.8%.

Early adopters of accountability laws

Drs. Hinshaw and Scheffler peg these regional differences squarely to education policy. When President George W. Bush signed the No Child Left Behind legislation into law in 2001, 30 states had already passed similar consequential accountability statutes. And many others had passed laws requiring students to take proficiency exams to qualify for high school graduation. It turns out that far more states in the South had passed accountability laws before NCLB (15 out of 17), and more had passed mandatory high school exams (13 out of 17) than any other geographical region.

We’ll examine in more detail the work Drs. Hinshaw and Scheffler have done when their book, which looks more broadly at all the factors that influence ADHD diagnoses, comes out early next year. But this correlation between accountability laws and the rate of ADHD diagnosis illustrates the importance of investigating the forces that influence who gets diagnosed and with what.

“We have to realize that as real as these disorders are, the diagnosis depends upon behavior,” explains Dr. Hinshaw. “We don’t have a laboratory test, and so diagnosis is always going to have a subjective component: Does this child’s behavior fit into this classroom, or fit into this family or this culture?”

School expectations drive diagnoses

This doesn’t mean that ADHD isn’t a real disorder. If kids didn’t have to go to school, there would still be children who are unusually (or extremely) active, inattentive and impulsive—the key symptoms of ADHD. These are behaviors that cause serious problems outside of school, too, and a rigorous diagnosis in fact requires impairment in at least two settings. Nonetheless, changes in what we expect from children in school, and increased pressure to meet those expectations, can be expected to have consequences in who gets diagnosed.

This isn’t unique to ADHD, Dr. Hinshaw notes. “Psychiatric pathology is part of an ecological framework. The condition is real, but it’s the fit of the person into the niche that often makes the difference whether there is a diagnosis or not.”

Accountability laws may be only one of the environmental factors shaping the rate of ADHD diagnoses, but it’s an important start, particularly if it focuses the attention of the community that’s concerned about these diagnoses in a constructive way.

“This is correlational epidemiological research,” Dr. Hinshaw cautions. Correlation, the saying goes, does not imply causation. “But it’s close to a smoking gun for us.”

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