When making a decision on what to buy, professional purchasers are continuously faced with the challenge of juggling price versus functionality/quality. Not infrequently, when drawing up the RFP documents it will be stated that some evaluation criteria are weighted, in other words they are more important than others. Weightings are inherently risky. A variety of devices have been concocted to try to avoid the problems presented by weighting criteria. One is to award the contract on a dollar per point basis. Another approach is to use a two or three envelope system. In a two-envelope approach, the functional scores of the various bidders are first tabulated to determine whether (and which) bidders satisfy some minimum functional threshold. Once the passing bidders have been determined, the financial scores of the bidders are determined and the contract is awarded to the qualifying bidder who submits the lowest price.

Statistical data
Performance evaluation
Methods