In the fall of 2004, there was a shortage in flu vaccine in the United States after it was discovered that vaccines from one of the manufacturers were contaminated. The New England Journal of Medicine reported on a study that was done to see whether a smaller dose of the vaccine could be used successfully. If that were the case, then a small amount of vaccine could be divided into more flu shots. In this study, the usual amount of vaccine was injected into half the patients, and the other half of the patients had only a small amount of vaccine injected. The response was measured by looking at the production of antibodies (more antibodies generally result in less risk of getting the flu). In the end, the lower dose of vaccine was just as effective as a higher dose for those under 65 years old. What more do we need to know to be able to conclude that the lower dose of vaccine was equally effective at preventing the flu for those under 65?