Evidence is the bread and butter of science. Reaching a scientific conclusion of any kind requires observation and measurement—ideally, the careful, repeated observation and measurement known as empirical evidence.
Evidence can take many forms, because research itself can take many forms. Sometimes, evidence may appear pictorially as a chart or graph. Pay careful attention to the labels and scales on graphs and charts, because just like words, visuals can mislead, as well as tell hidden stories.
Whatever form evidence takes, it's likely to be at least partly numeric. Alas, it's at precisely the moment when numbers appear that most people begin to tune out. That's unfortunate because numbers can't (usually) lie, which is why looking at the actual evidence can be most illuminating in evaluating a claim. For starters, how much data was collected? You don't need a degree in statistics to know that the more people there are involved in a study, the less likely it is that the results are just chance.
Sometimes, a claim may be made with no empirical evidence at all. File these claims under “S” for speculation. In other cases, a claim may rest on evidence that is limited or downright scanty. In paleontology, for example, where preserved specimens of ancient life are few, entire theories may rest precariously on the discovery of a single bone. In physics, string theory redefines the universe without any evidence at all. String theory holds that everything in our universe results from vibrations of miniscule strings, but no one has figured out how to test if the theory is true.