Which estimating technique?

This paper presents a unified view of the relationship between (1) quantity and (2) price generating mechanisms in estimating individual prime construction costs/prices. A brief review of quantity generating techniques is provided with particular emphasis on experientially based assumptive approaches and this is compared with the level of pricing data available for the quantities generated in terms of reliability of the ensuing prime cost estimates. It is argued that there is a tradeoff between the reliability of quantity items and reliability of rates. Thus it is shown that the level of quantity generation is optimised by maximising the joint reliability function of the quantity items and their associated rates. Some thoughts on how this joint reliability function can be evaluated and quantified follow. The application of these ideas is described within the overall strategy of the estimator's decision - "Which estimating technique shall I use for a given level of contract information? - and a case is made for the computer generation of estimates by several methods, with an indication of the reliability of each estimate, the ultimate choice of estimate being left to the estimator concerned. Finally, the potential for the development of automatic estimating systems within this framework is examined.