The likelihood of the occurrence of some event or outcome is referred to as:

A) reactivity.
B) reliability.
C) variability.
D) probability.

Probability

A measure of the likelihood that an event will occur, represented numerically between 0 (impossible) and 1 (certain).

Reactivity

The phenomenon in which the presence of an observer or the awareness of being observed alters the behavior of those being observed.

Reliability

The consistency of a measure or instrument, such that it yields the same results under consistent conditions across multiple trials.