I found these citations in a paper on the first page of Google. I apologize but I have not verified them.

Fayyad J, De Graaf R, Kessler R, et al. Cross-national prevalence and correlates of adult attention-deficit/hyperactivity disorder. Br J Psychiatry. 2007;190(5):402–409.

https://scholar.google.com/scholar_lookup?journal=Br+J+Psychiatry&title=Cross-national+prevalence+and+correlates+of+adult+attention-deficit/hyperactivity+disorder&author=J+Fayyad&author=R+De+Graaf&author=R+Kessler&volume=190&issue=5&publication_year=2007&pages=402-409&pmid=17470954&

Retz W, Retz-Junginger P, Thome J, et al. Pharmacological treatment of adult ADHD in Europe. World J Biol Psychiatry. 2011;12(suppl 1):89–94.

https://scholar.google.com/scholar_lookup?journal=World+J+Biol+Psychiatry&title=Pharmacological+treatment+of+adult+ADHD+in+Europe&author=W+Retz&author=P+Retz-Junginger&author=J+Thome&volume=12&issue=suppl+1&publication_year=2011&pages=89-94&pmid=21906003&

Newcorn JH, Weiss M, Stein MA. The complexity of ADHD: diagnosis and treatment of the adult patient with comorbidities. CNS Spectr. 2007;12(suppl 12):1–14. quiz 15–16.

https://scholar.google.com/scholar_lookup?journal=CNS+Spectr&title=The+complexity+of+ADHD:+diagnosis+and+treatment+of+the+adult+patient+with+comorbidities&author=JH+Newcorn&author=M+Weiss&author=MA+Stein&volume=12&issue=suppl+12&publication_year=2007&pages=1-14&