How such statements are to be applied is entirely up to the cultural context. I'm not speaking out of my ass here, the rates differ massively between European countries and the US (and across US states and across EU countries), largely due to the different notion of what would be 'significant'.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1525089/

Attention-deficit/hyperactivity disorder (ADHD) is a behavioral disorder that affects up to 1 in 20 children in the USA. The predominance of American research into this disorder over the past 40 years has led to the impression that ADHD is largely an American disorder and is much less prevalent elsewhere. This impression was reinforced by the perception that ADHD may stem from social and cultural factors that are most common in American society. However, another school of thought suggested that ADHD is a behavioral disorder common to children of many different races and societies worldwide, but that is not recognized by the medical community, perhaps due to confusion regarding its diagnosis and/or misconceptions regarding its adverse impact on children, their families, and society as a whole. In this article we present the available data, with a view to determining the worldwide prevalence of ADHD. A total of 50 studies were identified from a MEDLINE search for the terms ADHD, ADD, HKD, or attention-deficit/hyperactivity disorder and prevalence combined, for the years 1982 to 2001. 20 were studies in US populations and 30 were in non-US populations. Analysis of these studies suggests that the prevalence of ADHD is at least as high in many non-US children as in US children, with the highest prevalence rates being seen when using DSM-IV diagnoses. Recognition that ADHD is not purely an American disorder and that the prevalence of this behavioral disorder in many countries is in the same range as that in the USA will have important implications for the psychiatric care of children.