Empirical data or evidence is proof for an outcome that can be challenged or disproven through processes of replication and verification. It is based on the scientific method (including testing, experimentation, and observation). In the sciences and mathematics, empirical data follows a hypothesis through stages of inquiry, whether in a laboratory, physical testing, or a logical train of thought, to a conclusion that confirms the hypothesis or rejects it in order to develop a new hypothesis. Empirical evidence (direct observations or experiments) can be analyzed quantitatively or qualitatively:
QUALITATIVE DATA is data that can be observed but not measured (by smell, taste, color, appearance, and/or quality). Examples include surveys, classroom observation notes, and interviews.
QUANTITATIVE DATA is data that can be measured or counted. Examples include length, temperature, cost, and sound levels.
MIXED METHODS refers to the combination of qualitative and quantitative data to test a hypothesis. This method is common in the social sciences.