People's attitudes are based on the relatively few, stable values they hold. Kluckhohn and Strodtbeck's (1961) Values Orientation Theory proposes that all human societies must answer a limited number of universal problems, that the value-based solutions are limited in number and universally known, but that different cultures have different preferences among them. Suggested questions include humans' relations with time, nature and each other, as well as basic human motives and the nature of human nature. Kluckhohn and Strodtbeck suggested alternate answers to all five, developed culture-specific measures of each, and described the value orientation profiles of five SW USA cultural groups. Their theory has since been tested in many other cultures, and used to help negotiating ethnic groups understand one another, and to examine the inter-generational value changes caused by migration. Other theories of universal values (Rokeach, Hofstede, Schwartz) have produced value concepts sufficiently similar to suggest that a truly universal set of human values does exist and that cross-cultural psychologists are close to discovering what they are.