### Validity

Statistical technique used to determine if a test is actually measuring what it is intended to measure.

### Variability

The degree to which a distribution of scores vary around the mean. High variability means scores are spread wider apart and low variability means scores are relatively close together. Typical ways of determining variability are the range, interquartile range, semi-interquartile range, variance, and standard deviation.

### Variable

Any factor which has the potential to influence another factor in a research study.

### Variable Interval Schedule

A schedule in which the reinforcement is presented after a varying amount of time.

### Variable Ratio Schedule

A schedule in which the reinforcement is presented after a varying number of responses.

### Variance

A measure of spread within a distribution (the square of the standard deviation).

### Vicarious Reinforcement

The reinforcement that occurs as a result of watching a model get reinforced for a specific behavior or series of behaviors.