This is an opinion piece by one author. It has no study sample of its own. It pulls together earlier reviews and studies of people with ADHD, both adults and children followed into adulthood, and sets them next to people who had frontal lobe injuries or traumatic brain injuries.
The author says the answer to whether ADHD involves executive function problems depends on how those problems are defined and measured. When lab tests are used, ADHD groups do worse as a whole, especially at holding back responses and holding information in mind. But when people are looked at one by one, only a minority show clear problems (35 to 50%).
Lab tests and everyday rating scales tend not to line up. Any single test shares very little with how a person is rated in daily life (0 to 10%), and the link is often not meaningful. Even the best mix of tests shares only about 12 to 20%. In brain-injured patients watched during daily tasks, tests explained about 9 to 15% of real-world problems, or less. A test built to feel more like daily life raised this only to about 16%.
Because ratings track daily life better than tests do, the author argues that evaluations should use rating scales, interviews, or direct observation.
Source: Barkley R. Is Executive Functioning Deficient in ADHD? It Depends on Your Definitions and Your Measures. The ADHD Report (2011). doi:10.1521/adhd.2011.19.4.1