Threats to Validity

From a research design standpoint, the simplest way to understand threats to validity is that a hypothesis might be tested in a manner other than what the researcher had intended—a situation not to be confused with the researcher's failure to obtain the result he or she had expected. Much is presupposed in this distinction. Research is not a linear extension of common sense or everyday observation but rather requires a prior theory or paradigm that yields an appropriate hypothesis, on the basis of which the researcher selects relevant variables that are then operationalized and manipulated in an environment of the researcher's creation and control. Under these circumstances, two matters of validity arise: first, the reliability of the outcomes vis-à-vis other experiments of similar design, and ...