"A ratio of count per observation time; often expressed as count per standard unit of time and calculated by dividing the number of responses recorded by the number of standard units of time in which observations were conducted" (Cooper, Heron, & Heward, 2007, p. 85).

"A ratio of count per observation time; often expressed as count per standard unit of time and calculated by dividing the number of responses recorded by the number of number of standard units of time in which observations were conducted" (Cooper et al, 2007, p. 85).

"A measure of the total extent of time in which a behavior occurs" (Cooper et al, 2007, p. 79).

"A measure of temporal locus; the elapsed time from the onset of a stimulus (e.g., task direction, cue) to the initiation of a response" (Cooper et al, 2007, p. 80).

"...the elapsed time between two successive responses" (Cooper et al, 2007, p. 80).

"A ratio formed by combining the same dimensional quantities such as count or time; expressed as a number of parts per 100; typically expressed as a ratio of the number of responses of a certain type per total number of responses. A percentage represents a proportional quantity per 100" (Cooper et al, 2007, p. 701).

"A special form of event recording; a measure of the number of responses or practice opportunities needed for a person to achieve a pre-established level of accuracy or proficiency" (Cooper et al, 2007, p. 87).

"simple, logical explanations must be ruled out, experimentally or conceptually, before more complex, or abstract experimentations are considered" (Cooper, Heron, & Heward, p. 22).