in cost estimation stage, different estimations include:
Bottom-up estimation. in this estimation which yields more correct results, detailed and documentary, but time-consuming data are used.
comparable estimation. in this estimation historical cost data of similar projects and previous similar activities are used for estimating total cost of the project. this method has lower cost than previous one but needs experts,ideas and judgments.
parametric estimation. this estimation uses math models, finger tip rules, and cost estimation relations to estimate the costs of project elements.cost estimation is the correlation of cost and work amount which needs computer tools. thus, at this stage, the basis of cost management is information technology.