It’s all over the wire today that there are quan­ti­ta­tive dif­fer­ences to be found in brain devel­op­ment between kids who have been diag­nosed as ADHD and those who have not.

A lon­gi­tu­di­nal study by NIMH and McGill University seems to show that nearly 225 kids aged 6 to 16 have less dense neu­ronal struc­ture if they’ve also been diag­nosed as hav­ing ADHD, while the same num­ber of kids who lack the diag­no­sis appear to have under­gone nor­mal brain development.

While on the sur­face this appears to be a pos­i­tive cor­re­la­tion between ADHD and unusual brain devel­op­ment, there’s a seri­ous flaw in the study which I found admit­ted to in only one piece men­tion­ing it:

About 80 per­cent of those with atten­tion prob­lems were tak­ing or had taken stim­u­lant drugs, and the researchers did not know the effect of the med­ica­tions on brain development.

In other words we still don’t know if putting ADHD-​​diagnosed kids on drugs is a good idea, or if it might even worsen the prob­lem. There was no unmed­icated con­trol group, and because of the diag­noses, there wasn’t even a pos­si­bil­ity of a double-​​blind com­par­i­son. There was no indi­ca­tion of nor­mal­iza­tion of other fac­tors (such as diet, amount of phys­i­cal activ­ity, time spent read­ing ver­sus watch­ing TV or play­ing video games, etc.) and the researchers them­selves have said that it took years for the devel­op­ment dif­fer­ences to even be noticed:

Doctors can­not diag­nose atten­tion deficit or any other psy­chi­atric dis­or­der with imag­ing tech­nol­ogy, in part because brains vary so much that a sin­gle series of images can sel­dom reveal who has a dis­or­der. The new find­ings sug­gest that search­ing for a clear abnor­mal­ity or flaw is the wrong approach, at least for atten­tion problems.

So what we appear to have here is a cor­re­la­tion, of sorts, but absolutely no indi­ca­tion of causative fac­tors, and no sig­nif­i­cant con­fi­dence in draw­ing a con­clu­sion about the effi­cacy — or desir­abil­ity — of med­i­cines in treat­ing ADHD diagnosis.

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