Dr. prentice, principal of an elementary school, instructs her teachers to employ a new aggression-reduction program with the second graders and to keep using it on that group of students for the next three years. she finds that, relative to the start of the program, aggression in that group of students is down 35%. this example illustrates the possibility of as a plausible rival hypothesis.

Americans often speak of their country as one of several large regions.  these regions are cultural units rather than governmental units --  formed by history and geography and shaped by the economics, literature and folkways that all the parts of a region share. what makes one region different from another? a region's multicultural heritage as well as distinct demographic characteristics like age and occupation make regions different and special. within several regions, language is used differently and there are strong dialects. there are also differences in outlook and attitude based on geography.