Statistical Acceptance
The statistics that let an agency accept work on a limited number of tests: the normal distribution, acceptance plans and control charts.
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Acceptance Plan Components
Acceptance sampling has been in general use for well over 60 years (Montgomery, 1997). Therefore, the theoretical underpinnings behind acceptance sampling are well proven.
Acceptance Plan Basics
In general, a statistical acceptance specification is simply an acceptance procedure.
Acceptance Plan Categories
Statistical acceptance plans can be categorized according to their specification limits and decision criteria structure. Depending upon the category, different components of the plan will carry different levels of importance.
Control Charts
In general, control charts are used to plot production values and variation over time.
HMA Control Chart Example
The following is a simple example of a set of control charts that could be used for HMA in-place air voids. Actual paving data from the Washington State Department of Transportation (WSDOT) is used for all charts.
Normal Distribution
The normal distribution is a data distribution that can be used to describe many types of measurements in engineering. Basically, a normal distribution is a bell shaped curve.
Verification of Contractor Test Results
How agencies verify contractor QC results before using them in acceptance: independent samples, the F-test and t-test, split samples, and failed comparisons.