An expert system is being developed to help assure the quality of data in the Consumer Price Index (CPI). The system replicates the reasoning of Commodity Analysts determining if a substitute product is comparable to a product priced in the previous month. If comparable, its price can be considered in producing the CPI. The system reasons with expertise directly entered by Commodity Analysts. To help the experts (Commodity Analysts) serve as their own knowledge engineers, they are provided with a skeletal system to which they add their knowledge of particular product categories. The system was tested on six months of CPI data. Results indicate that Commodity Analysts can accurately encode their own expertise and use the technology to detect their own oversights. The success of the current project may help other members of the government statistical community collect and review survey data using similar technology.