Last week we heard news that the FDA has approved the use of a medical device to aid in the diagnosis of ADHD, based on the electroencephalogram, or EEG—electrodes placed at different points around the scalp to measure the electrical activity in your brain. In theory, this sort of innovation is exciting—the practical application of advances in neuroscience that show us that real brain differences underlie psychiatric disorders. These illnesses are now diagnosed by so-called “subjective” means: clinical interviews, rating scales, observation. The objective “blood test”—or in this case “brainwave test”—for ADHD or depression or autism is in many corners the Holy Grail of psychiatric research.

But even those who search for that prize acknowledge that we aren’t there yet, and experts are skeptical of the device’s readiness for primetime. The company who makes it contends that it helped clinicians make a better diagnosis than they would have without it, but doesn’t offer any data on that claim. And EEG researchers aren’t confident in the technique’s accuracy without larger studies and more data. (Dr. Michael Milham, director of the Center for the Developing Brain at the Child Mind Institute, points to a recent study which concludes that the EEG method used by the device does not have diagnostic value in ADHD patients.) Finally, there is the question of exactly what the device measures. If at best the test replicates the observations of a trained clinician, it could simply be identifying symptoms—symptoms that can indicate a variety of disorders, and require the interpretation of a trained clinician. “What’s the point?” one ADHD expert asks The New York Times.

But it got FDA approval! That’s not as hard as people think, says Dr. Milham, particularly with a passive, non-invasive technique. The fact is that the FDA weighs a drug or a device’s benefit against its risk. In this case, it seems by many accounts that the agency was convinced there wasn’t any reason not to approve it. But that doesn’t mean it’s the answer, though we hope that one day EEG and other technologies like MRI and genotyping can be fully leveraged to get the best care to kids who need it.