Statistically Based Methods for Verification Testing

State highway agencies currently use split-sample and independent-sample verification procedures for the purpose of comparing test results or verifying the contractor’s overall construction process in independent assurance (IA) programs and quality assurance (QA) construction specifications. Sampling procedures are reviewed, and new statistically based methods for developing comparison procedures in both IA programs and QA specifications are presented. The statistically based approach determines an appropriate mean difference between either split-sample test results or independent-sample verification results by recognizing sample size, field variability, and inherent risks. A practical application is given using collected field data from hot-mix asphalt (HMA) construction projects. State highway agencies and contractors will benefit from an understanding of the statistical concepts involved with split-sample and independent-sample comparison procedures and of what information an agency needs to determine if a contractor’s overall test results are accurate. The concepts and procedures presented can be applied to all areas of highway construction involving split-sample and independent-sample verification tests, such as base materials, concrete structures and pavements, and HMA pavements.