Which of the following is NOT a factor influencing variability of testing?

Random sampling methods are designed to minimize bias and ensure that every member of a population has an equal chance of being selected. However, while these methods are important in achieving a representative sample, they do not inherently influence the variability of testing outcomes. The focus of random sampling is on the selection process rather than on the factors that affect the consistency and reliability of the test results themselves.

In contrast, the other factors listed—equipment used, personnel performance, and test method adherence—directly affect the precision and accuracy of test results. For example, equipment can introduce variability due to calibration issues or operational differences. Personnel performance can lead to variability if the testers have differing levels of skill or familiarity with procedures. Likewise, adherence to test methods is critical; any deviation can result in inconsistent outcomes. Therefore, while sampling methods are essential for obtaining data, they do not directly contribute to the variability of testing in the same way that the other options do.