... Correlational research involves measuring such relations in the most straightforward manner.
However, experimental research is not any different in this respect.
For example, the previously cited experiment comparing white cell count  in males and females can be described as looking for a correlation between two variables: Gender and WCC.
Statistics does nothing else but help us evaluate relations between variables. Actually, all of the hundreds of procedures that are described in this online textbook can be interpreted in terms of evaluating various kinds of inter-variable relations.