Many non-scientists are increasingly confused and dismayed by the constantly changing advice that comes from medical, nutritional and other researchers. Some of that confusion is due to the quality of the evidence, which is dependent on a number of factors, while some is due to the very nature of science: We form hypotheses and then perform experiments to test them. As the data accumulate and various hypotheses are rejected, we become more confident about what we think we know. But uncertainty may arise from the current state of scientific investigation: The results of experiments often cannot be replicated, and similar experiments by different researchers often yield conflicting results. Read more.