The improving survival rates of extremely low, very low, and low birth weight (LBW) and premature (PM) infants are good news. Scientifically, they raise complex questions about trends in the incidence of neurodevelopmental conditions,1 from severe injuries like cerebral palsy, now declining after earlier increases in incidence,2 to subtler yet also disabling and costly conditions like attention-deficit/hyperactivity disorder (ADHD), whose true incidence likewise may not have increased in the past 15 years.3 

In the accompanying meta-analysis by Franz et al,4 the magnitude of the association of LBW/PM with ADHD is striking; at a risk increase of ∼300%, it is perhaps the strongest single risk factor for ADHD of any type (biological or environmental) now known. At this effect size, LBW/PM would characterize a substantial portion of ADHD cases. Researchers of ADHD populations who can clarify how many patients had LBW/PM, and who can include more in-depth...

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