Graziano and Raulin (8th ed)Graziano & Raulin
Research Methods (8th edition)

Glossary Items Starting with "V"

Having validity.

Major concept in research that has several specific meanings (internal validity, external validity, construct validity, statistical validity). In a general sense, validity refers to the methodological and/or conceptual soundness of research (e.g., "Does this experiment really test what it is supposed to test?").

Differences among participants on any given variable.

Any characteristic that can take on different values. 

Summary statistic that indicates the degree of variability among participants. The variance is essentially the average squared deviation from the mean and is the square of the standard deviation.