Statistics are only as good as the representativeness of the sample. An important point with both facts and statistics is not to confuse either with conclusions or inferences drawn about them. Any conclusion or inference is a contention which is subject to debate. For example, the downfall of communism in Europe is a fact. That it was caused by the Reagan policy of escalating the arms race is a contention.
Authorities Citing authorities on the subject is a weaker form of evidence which varies in strength.
On the one hand, the expert's statement may be reflecting a large body of facts and statistics on the topic or the specific empirical results of a sound research project. As such the expert's statement is a strong form of evidence. Because examples are frequently little more than a single case, they alone cannot confirm a hypothesis or assertion, but they still are of value. First, examples are very useful for illustrating a point. Examples put substantive meat on the bones of the generalization.