A newspaper story in Knight Ridder Newspapers described an experiment in an article with the headline “Doctor Dogs Diagnose Cancer by Sniffing It Out.” In the experiment researchers trained dogs to identify people with breast or lung cancer. The dogs were trained to lay down if they detected cancer in a breath sample. After the training, dogs sniffed different breath samples of people with and without cancer. Impartial observers watched the dogs and decided when the dog identified a person as having cancer. Researchers then revealed the condition of the person who gave the breath sample and determined if the dog had correctly identified the presence of cancer. The newspaper states, “The researchers blinded both the dog handlers and the experimental observers to the identity of the breath samples.” What is meant by the last sentence?