What is evidence?

Students need to appreciate that scientific theories must be supported by evidence. But what is evidence?

Evidence is usually considered to be data from survey or experiment or previous research. However, realistically it relates to more than just hard facts. It embraces the results of analyses and consultations and so includes opinions, judgments and beliefs. The experimenter effect is well known when scientists interpret their results.

The evidence base for a theory is not static; it changes constantly as scientist's understanding changes and as new research results come in. When the evidence isn’t clear cut scientists will assign a level of confidence to their prediction from the data. You can read more about this in Understanding the Maths