Mark Creighton is a technician working in a radiobiology laboratory. His current project entails assaying prostaglandin excretion in rats that have been treated with various radioprotective agents before exposure to gamma radiation. Prostaglandin measurements are taken with an autoanalyzer, a machine that automatically dispenses and mixes reagents used in the assay. In one of the experimental runs, six of the ten assays show a reasonably clear, positive correlation between the dosing of a radioprotective drug and prostaglandin excretion. Four of the assays show no such correlation. Upon hearing the results, Mark's supervisor explains that the assay equipment is highly delicate, and unless conditions are ideal and the reagents very fresh, erroneous results can be obtained. He tells Mark that the results showing no correlation will not be considered in the write-up of the research because it is clear that they are not valid. The supervisor asks Mark to freshen the reagents more frequently and to continue collecting data.