Presenting concepts generally applicable only to small rural regions or to local economies, this publication explains multipliers, shows how they are used in calculating impacts, and provides some criteria for determining whether a given multiplier can be used in a specific situation. Following a discussion of aggregate multipliers, which lump different types of businesses together, and disaggregate models, which divide the economy into sectors with a multiplier for each sector, is a review of problems frequently encountered in applying multipliers to community change (interchanging multipliers, double counting, pyramiding, and confusing multipliers with other economic measurements, e.g., turnover and value added). The criteria stated for determining the appropriateness of a multiplier include the basis for the multiplier, i.e., local data, primary or secondary data; aggregate versus disaggregate multipliers; the basis for an employment multiplier, e.g., number of jobs or full-time equivalent; the base year on which the economic model was formulated; the function of a multiplier; the extent of the impact in relation to the size of the affected industry on which the multiplier is based; the calculator of the multiplier; and the inclusion of household income as a sector similar to the business sectors in the local economic model. (NQA)