Reduced form price equations were estimated to compare market demand responses from two data sources: U.S. Department of Agriculture (USDA) beef price and price spread data per revisions in 1978 and per revisions in 1990. The latest revisions were necessary to account for changing beef industry technology and product consumption in the 1980s. Results indicate the elasticities of retail and derived demands average about 25 and 17% lower, respectively, when using the 1990 revised data. Trends and lag adjustments played an important role. The analyses suggest careful interpretation of demand responses when time series data lag technology conditions in the market.