**Unconditional Positive Regard**The nonjudgmental empathy and respect for another person.

**Unconditioned Response**

The response in a stimulus-response chain that is naturally occurring as opposed to learned.

**Unconditioned Stimulus**

The stimulus in a stimulus-response chain that is naturally occurring as opposed to learned.

**Unconscious **

According to Freud, the area of the psyche where unknown wishes and needs are kept that play a significant role in our conscious behavior.

**Upper Confidence Level**

The upper limit of a confidence interval. If prediction states that the true score falls between 80 and 90, then the upper confidence level is 90.

**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.

**WAIS-III**See Wechsler Adult Intelligence Scale, Third Edition.

**Weber’s Law**

The amount of change necessary to detect a different in a stimuli must be staged in a percentage since recognition of the change is relative to the characteristics of the initial stimulus (e.g., a one pound change in the weight of a pencil would be more easily recognized than a one pound weight added to a 300 pound barbell because it represents a much greater percentage of the total weight).**Wechsler Adult Intelligence Scale, Third Edition **

An objective measure of intelligence. The Stanford-Binet test is also used, has very similar validity, but is not as popular.

**Wernicke’s Aphasia**

Aphasia resulting from damage to the Wernicke’s area of the frontal lobe. Affects written and spoken language.

**Yerkes-Dodson Law**Theory arguing that for performance to be optimal, the amount of arousal required must be optimized. Too much or too little stimulation will result in a poorer performance.

**Zero Correlation**the absence of a relationship between two or more variables as determined by a correlational statistic. Often abbreviated as ‘r=0.’

**z-score**

a standard score that sets the mean to zero and standard deviation to one.

**z-test**

The statistical formula to determine the z-score of a particular raw score.

*Source: Allpsych Online*