Factor of reliability of cost implication and practical limitation

- Main source cost data are obtain from contractor prices which is subject to consideration variable * from contractor to contractor * Project to project * district to district * Over a period of time * Lack of concidence between the unit of productioc cost and unit of design cost account . * Skilled judgement is neccessary when extracting the cost data from price BQ * Cost information used by the QS is advisable to use average price rather than the lowest * Additional cost due to specific design and abnormal requirement are in forecasting stage * Difficult of predicting operatinal cost , and regional different ,etc * Unit cost is made up of standard cost within determinable parameter . * Factor of consideration : - Type of project - Size of project - Location of project - Stability of material - Availability of labour - Fixed price tender - Method of pricing preliminaries - Climate of the industry * Necessary to know the condition of the prices - Price different in billes rate are not neccessary due to mistake