Factor of reliability of cost information and practical limitation .

- Main sources of cost data are obtain from the contractor price which is subject to consideration variables * From contractor to contractor * Project to project * District to district * Over a period of time * Lack of concidence between the unit production cost and unit design cost account * Difficult of predicting operational times , regional different and etc . * Additional cost due to specific design , abnormal requirement are forecasting stage . * Factor of consideration -Type of contract -Project location -Size of project - Availability of labour -Stability of material prices -Whether fixed price tender - Method of pricing - Special requirement as to speed * Must interpret the cost appropriate before use . * Cost information used by QS obtained from price BQ and is advisable to use average price rather than lowest . * Prices different in billes rate are not necessary due to mistakes in estimating . * * Unit cost is made up of standard of within determinable parameter