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Introduction to Percent Within Limits: The Quality Measure of Choice Workshop
Agenda
9:00 AM through 4:00 PM
Intended Audience: State highway agency and FHWA division personnel responsible for developing and overseeing quality assurance specifications, as well as pavements and materials engineers.
Module 1: Welcome
In this module participants discuss their experience and questions about PWL along with a discussion of issues unique to the highway industry, variability, and outlines the rest of the course. Module 2: Basic Statistics
This module provides a review of the basic statistical concepts that will be used in the workshop including terminology and definitions, sample size, random sampling, standard normal distribution, and normality assumptions. Module 3: Overview of Quality Measures
This module describes various quality measures* historically used in highway construction through terminology and definitions used in quality. We will include examples of uses, advantages, and disadvantages and to some degree show a progression of improvements in the quality measures.
* Average, Moving average, Average deviation (AD) from target, Average absolute deviation (AAD), Conformal index (CI), Percent defective (PD)/Percent within limits (PWL)
Module 4: Why is PWL Better
By further comparing and contrasting the quality measures discussed in the previous module, we explain why PWL is considered the quality measure of choice. Module 5: Computing PWL
This module begins with a discussion on the difference between the true PWL and the PWL estimate. Then we proceed to show how to compute the PWL estimate using the concept of quality index. We also demonstrate the effect of the number of samples on the PWL estimate. Module 6: Setting Specifications Limits
This module focuses on the difference between specification limits and acceptance limits and the relationships to acceptable quality level (AQL) and rejectable quality level (RQL). It also describes methods for establishing specification limits. Module 7: Payment Issues
In this module we explain fundamentals of payment and describe the difference between stepped and continuous acceptance plans. We also discuss payment nuances in reference to single versus multiple quality characteristics and correlated quality characteristics. Module 8: Implementation and Wrap Up
In this last module we discuss some key challenges of implementing PWL and provide information about resources available for implementation. We conclude by going over the questions raised at the beginning of the workshop and by addressing any other questions that may have come up.
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