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Quality Assurance Software for the Personal Computer, Demonstration Project 89
Statistic based QA specifications and acceptance procedures have been implemented without fully understanding the risks involved to both the State Transportation Department (STD) and the contractor. The two types of risks discussed when developing Quality Assurance (QA) specifications are the seller's (contractor) risk (α) and the buyer's (department) risk (β). The acceptable level of α and β risks is a subjective decision that can vary from department to department. A properly developed QA acceptance plan takes these risks into consideration in a manner that is fair to both the department and contractor. It is estimated that few departments have developed and evaluated the risk levels associated with their acceptance plans.
The selection of the number of samples required by a department may need to be modified based on an analysis of risks. The final decision regarding sample size per lot cannot be made until an evaluation of risks has been completed. An attempt should be made to balance the risk between the contractor and department while holding the risk to both at a reasonable level. This means that a large number of samples may be required. If the risks cannot be held to a reasonable level for both the department may have to accept a disproportionate level of risk.
For Percent Within Limits (PWL) or Percent Defective (PD) acceptance plans, computer simulation is almost always used to develop a and b risks, Operating Characteristic (OC) and Expected Pay (EP) curves. The OCPLOT computer program that was developed as a part of FHWA Demonstration Project No. 89 is able to develop OC and EP curves, run simulations on the effect of the variability of the individual lot pay factors on the final pay factor determination, and create histograms.
"Quality Assurance Software for the Personal Computer, Demonstration Project 89," Publication No. FHWA-SA-96-026, Federal Highway Administration, Washington, DC, May 1996.
Abstract: Demonstration Project 89 on Quality Management was created to provide guidance on the use of practical and effective quality assurance procedures for highway construction projects. The intent is to assure that the level of quality designed into the plans and specifications is actually achieved in the finished product. One part of this effort is the distribution of a software package consisting of several interactive programs developed for use on a computer. These DOS based programs enable the user to analyze both pass/fail and pay adjustment acceptance procedures, construct operating characteristic curves, plot control charts, experiment with computer simulation, perform statistical comparisons of data sets, demonstrate the unreliability of decisions based on a single test result, and explore the effectiveness of stratified random sampling. This comprehensive software package provides highway engineers with the necessary tools to learn why some statistical procedures are inherently superior to others and how to incorporate this knowledge into fair and effective construction specifications.
Note: The executable programs included with this publication are DOS based and therefore may not readily run from your computer if it is not set up to run DOS programs. Try loading these programs onto a 3.5" computer disc and run the programs directly from the disc or consult your computer specialist if you have problems executing the programs.
The seventeen (17) files included with Publication No. FHWA-SA-96-026 include:
Consult Publication No. FHWA-SA-96-026 for guidance on the use of these programs.
Although published in 1996, there has been limited availability and use of this group of programs for developing and evaluating QA acceptance plans. The programs have been provided here due to a greater emphasis recently placed on understanding, evaluating and reducing risks associated with QA acceptance plans created by State Transportation Departments. The use of this group of programs and the companion report is intended for a select group of individuals that understand QA specifications and acceptance plans in order to help them evaluate and validate their plans and understand how changes may affect the risks to both contractor and agency.