- valid
- Having
*validity*.

- 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?").

- variability
- Differences among participants on any given variable.

- variable
- Any characteristic that can take on different values.

- variance
- 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.