In Brazil, a birth cohort study was started in 1993 of 5249 persons who were followed from birth throughout childhood into adulthood up to age 18. About 80% of the total cohort was successfully followed. At age 11, they received an ADD screen which was repeated at age 18.
Overall 8.9% of the sample met ADD criteria at age 11. This prevalence increased to 12.2% at age 18. This observation would seem to support the view that ADD persists into adulthood in all patients; in fact some new cases are picked up.
This study used the concept of a diagnostic hierarchy, however, unlike almost all prior studies of adult ADD. It didn’t ignore other diagnoses. Thus, it assessed whether ADD was present in adulthood only in the setting of other diagnoses which can cause inattention, specifically mood (bipolar and MDD) and anxiety (GAD and social anxiety) conditions. When those other diagnoses were ruled out, and researchers assessed the presence of only ADD itself, without any other potential diagnostic causes, the adult prevalence rate fell by about one-half, from 12.2% to 6.3%.
Thus, to review, about 9% of children met ADD criteria. This rose to 12% of young adults at age 18. But this fell again to about 6% if ADD is defined as meeting ADD criteria and not having other psychiatric diagnoses that can cause inattention.
At first glance, even with this complex analysis, it would still seem that about 2/3 of children who had ADD persisted into adulthood: 9% at age 11 versus 6% at age 18.
However, this wasn't the case, because they weren't the same people.
Of children at age 11 who met ADD criteria, only 17% continued to meet those criteria at age 18. In other words, ADD went away in 83% of children by adulthood. This finding is consistent with over half a dozen course studies conducted prior to the introduction of medications for adult ADD. In that literature up to about the year 2000, the overall finding was that about 90% of children with ADD no longer met criteria by around age 20. This Brazilian study confirms that earlier literature.
It also throws some light on current debates about adult ADD, however, in that it still found a good number of young adults met ADD criteria, even though they didn’t have ADD as a child.
Thus, the second important observation here was that only 12.6% of the adult ADD cohort also had been identified as having ADD as a child in this prospective study where they had been assessed previously for ADD. In other words, 87.4% of adults who met DSM criteria for ADD as adults had not experienced it as a child.
How believable are these results and what do they mean? The authors refer to a recent meta-analysis of adult persistence of childhood ADD which fully agreed with their findings: adult persistence was less than 20% overall. They also refer to another large recent study which found only 5% persistence of childhood ADD when followed further into middle age adulthood.
The observation that about 5% of adults have impaired attention, which cannot be attributed to ADD or to other psychiatric conditions like mood and anxiety syndromes, is important. It’s important to emphasize that these persons do not have “ADD” because this study proves that their inattention is not persistence of childhood ADD.
So what do they have?
One possibility is that they experience “normal” inattention, in the sense that they are at the extreme of a normal curve for inattention. Since selective attention is a normal psychological trait, what we might appreciate is that attention exists on a normal curve, with most of us at the middle, near the 50th percentile. But two standard deviations to either side will represent about 5% of the general population, who are other overly-focused (which is consistent with obsessional or manic thinking) or under-focused (which is labeled “ADD” frequently).
This perspective, about normal variations in attention, has been described in November PL issue, and this study result can be interpreted as supportive of that interpretation.
It should be noted that these persons did have some clinical consequences of their inattention, such as increased criminal behavior, incarceration, and suicide attempts.
Importantly, personality conditions were not assessed, so the possibility that some of them had mood temperaments, as discussed in this issue, would also be present.
Further, prior research suggests that a subgroup of patients with childhood ADD later are diagnosable with antisocial personality, which could correlate with some of the findings in this study.