Answer:
Operational definitions.
Step-by-step explanation:
Operational definitions is a detailed, concise, precise and clear definition of a measure. It's applied when collecting data for a research, and it's a mandatory process, because this way the research will have precise defintion about the variables, which also determines the specific situation the researcher is going to study.
So, using operational definition of the variables, there won't be room for imprecise perspective in the research, and the investigator is gonna know specifically what is he or she studying.
Therefore, operational definitions completes the blank here.
When a researcher wants to correlate tension with depression, she develops tests that measure these two emotional states. The tests are her operational definitions of the variables she is interested in.