The Consumer Expenditure Survey (CES) series (formerly called the Survey of Consumer Expenditures) provides a continuous flow of information on the buying habits of American consumers and also furnishes data to support periodic revisions of the Consumer Price Index. The series consists of two separate surveys: (1) a quarterly Interview Survey in which each consumer unit in the sample is interviewed every three months over a 15-month period, and (2) a Diary Survey completed by the sample consumer units for two consecutive one-week periods. The Interview Survey was designed to collect data on major items of expense, household characteristics, and income. The expenditures covered by the survey are those that respondents can recall fairly accurately for three months or longer. A component of the Interview Survey is the Detailed Expenditure Files, which contain more detailed expenditure records than those found in the Interview Survey data. These files were released as a separate dataset from 1988 to 1993 and then were combined with the Interview Survey starting in 1994. A new Interview Survey questionnaire was introduced beginning in April 1991, resulting in significant changes to the 1991 Interview Survey data files. Several files, including Purchases of Household Appliances, Inventory of Household Appliances, Inventory and Purchases of Owned Vehicles, Disposal of Owned Vehicles, Trips and Vacations, and Vehicle Make/Model Codes and Titles, were moved to the Detailed Expenditure Files. The Diary Survey contains expenditure data for small, frequently-purchased items bought on a daily or weekly basis. Participants are asked to maintain expense records, or diaries, of all purchases made each day for two consecutive one-week periods. The unit of analysis for the Consumer Expenditure Surveys is the consumer unit, consisting of all members of a particular housing unit who are related by blood, marriage, adoption, or some other legal arrangement. Consumer unit determination for unrelated persons is based on financial independence.