In practice, firms are unable to derive definitive demand curves because of incomplete information. For this reason many firms use a COST-BASED PRICING formula for determining prices, but allow for the influence of demand by varying the profit mark-up (see DEMAND-BASED PRICING, COMPETITION-BASED PRICING).
There are various methods a firm can use to ‘forecast’ demand, including time series analysis, barometric indicators and econometric models. See SALES FORECASTING.