Empirical

A central concept in science and the scientific method is that all evidence must be empirical, or empirically based, that is, dependent on evidence or consequences that are observable by the senses. Empirical data is data that is produced by experiment or observation. It is usually differentiated from the philosophic usage of empiricism by the use of the adjective "empirical" or the adverb "empirically." "Empirical" as an adjective or adverb is used in conjunction with both the natural and social sciences, and refers to the use of working hypotheses that are testable using observation or experiment. In this sense of the word, scientific statements are subject to and derived from our experiences or observations.

Variations
In a second sense "empirical" in science may be synonymous with "experimental." In this sense, an empirical result is an experimental observation. In this context, the term semi-empirical is used for qualifying theoretical methods which use in part basic axioms or postulated scientific laws and experimental results. Such methods are opposed to theoretical ab initio methods which are purely deductive and based on first principles.

In statistics, "empirical" quantities are those computed from observed values, as opposed to those derived from theoretical considerations.

In economics, "empirical" generally refers to statistical or econometric analysis of numeric data. Other forms of observation-based hypothesis testing are not considered to be "empirics."

The use of the adjective empirical, especially in scientific studies using statistics, may also indicate that a particular correlation between two parameters has been found, but that so far, no theory for the mechanism of the connection is known.

In Chemistry the term empirical is used to refer to a molecular formula in its lowest common terms found in terms of element proportions and molar masses.