The science of psychology tries to develop explanations of human behavior through objective observations. The procedures or operations that we use to objectively measure a variable are known as its operational definition. The operational definition gives the variable meaning within a particular study.

Because the meaning of our study rests on how we objectively observe the construct or behavior of interest, developing a reliable and valid set of procedures for measuring our variables is crucial for the validity of any research study. Good operational definitions require that we first specify our constructs; developing reliable and valid operations is the last step of specifying constructs when we are designing our own studies.