Question: Distinguish between primary and secondary data, and identify the sources of each type. Primary data can be collected by the firm's own researchers or by independent marketing research companies. Three principal methods of primary data collection are observation, survey, and experiment. Secondary data can be classified as either internal or external. Sources of internal data include sales records, product evaluation, sales force reports, and records of marketing costs. Sources of external data include the government and private sources such as business magazines. Both external and internal data can also be obtained from computer databases.