* Empirical evidence: This is the most common and direct way to refer to the noun form.
* Empirical data: Similar to "evidence", this refers to the information gathered through observation and experimentation.
* Empiricism: This is a broader term that refers to the philosophical approach of relying on observation and experience.
* Empirical study: This refers to a specific research project that uses empirical methods.
* Empirical findings: This refers to the results of an empirical study.
The best choice will depend on the specific meaning you want to convey.