Testing is also quite selective. In developed countries, IQ tests are used to diagnose mental handicaps. In third world countries, they test their smartest in an effort to elevate the published IQ score for global consideration. China in particular is quite guilty of this. Further, IQ is trainable to an extent and consists of a broad range of categories. Jews excel at linguistic reasoning but are mediocre at spatial reasoning, but the linguistic score is the one touted so proudly.
IQ as a system to determine intelligence was always bound to fail. However, for its intended purpose to diagnose retards, it's an exceptionally good system. Don't use it to determine if the Japanese are smarter than Swedes or even if Peru and Bolivia are better than each other. Use it to show that any immigration from nations outside of the European and East Asian genetic blocks is a fool's errand.