Informally, we speak of a cross section of a population even if the group chosen is not statistically representative of the population as a whole. Thus you might say You meet a cross section of Americans when you travel by interstate bus, even though it is clear that some types of Americans are likely to be underrepresented among the people who ride interstate buses. When cross section is used in reference to the samples used in surveys and other investigations, the presumption is usually that the group has been chosen so as to be representative of the larger population, and here you must be more careful. Eighty-four percent of the Usage Panel finds the phrase representative cross section to be unacceptably redundant.
