Aggregation bias stems from the loss of detail that occurs when you aggregate a region's sectors before generating the multipliers. Multipliers are derived from output per worker averages, other value-added ratios, and the production functions of industries. When you aggregate a region's industries before generating multipliers, it has the effect of taking several individual Industries and combining them to form a totally new Industry. The production function and relationships of the new aggregated Industry becomes the weighted average of the individual production functions, with those industries with the greatest output levels having the greatest influence on the aggregated industry. Therefore, the new Industry's production function may not truly represent an industry being impacted. This creates aggregation-induced error, or bias. Thus, it is typically recommended to aggregate the impact results rather than the model itself. However, aggregating IMPLAN Sectors in a model can be useful for those who do not have specific Sector detail for their numbers or are working with a standard NAICS aggregation for their input data.