The most important reason to use operational definitions in psychological research is it

These are important because the measured variables must be defined to calculate them appropriately

Explanation:

An operational meaning is the declaration of the procedures which the researcher would use to calculate a particular variable, it is a description of the methods or ways a researcher should measure behaviors or qualities.

The need for operational concepts is important when collecting data of all forms. It is especially important when there is a decision about whether anything is right or wrong, or when there is a visual test where there is space for uncertainty.