Answer to Question 1
ANS: B
Evaluating the same specimen multiple times and applying statistics to the results determine precision or reproducibility. The SD describes the precision. The mean is the average result (assuming a gaussian distribution). Sensitivity describes how well a test identifies positive patients, whereas specificity is how well it identifies only positive patients.
Answer to Question 2
ANS: D
Shifts can occur when a new reagent is introduced. A fading light source would lead to trend error. If the instrument were calibrated incorrectly, then both controls should be out; likewise, operator error would result in both controls being unacceptable.