A reasoning flaw in which the supporting evidence comes from a sample, source, or context that is systematically unrepresentative of the population the conclusion describes. Classic LSAT example: a poll of Sports Illustrated readers used to conclude something about "the world" — SI readers skew American, English-speaking, and toward sports SI covers, so they cannot ground claims about global recognition. The flaw includes self-selected samples, survivorship bias, and any evidence gathered under conditions different from the conclusion's context.