Eliminating Bias in Construction Schedules to Measure Time

by Daniel G. Quackenbush, CCL Construction Consultants, United States,
Michael T. Callahan, CCL Construction Consultants, United States,



Document Type: Proceeding Paper

Part of: Excellence in the Constructed Project

Abstract: Schedules developed for use in managing the construction process which are accurate for that use are not necessarily sufficiently accurate to measure and evaluate delays and changes to the construction project. Construction schedules inherently contain the bias of the scheduler who developed them. This bias is not necessarily intentional or meant to distort or exaggerate delays. CPM scheduling can be done in one of two formats, precedence or I-J. Typically, I-J scheduling does not lend itself to substantial additional bias because of its highly structured nature. Precedence scheduling tends to be more 'creative' and has greater flexibility in style and approach to the scheduler. Various computer softwares use different algorithms to calculate early start, early finish, late start and late finish dates in the precedence diagramming method. This results in different completion dates for the same schedule. I-J or arrow node type scheduling use very similar algorithms in the calculation process which results in most software programs producing identical start and finish dates. The most drastic differences among precedence software programs occur in the use of leads, lags, finish to finish relationships and open starts and finishes. These and other aspects of the subject are discussed.

Subject Headings: Scheduling | Computer software | Project delay | Algorithms | Construction methods | Data processing

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