1) The rate of an operant before any known conditioning. For example, the rate of key pecking before a peck-food contingency has been established.

2) How often, how rapidly, or how forcefully a response was made before a treatment or program was started. Roughly speaking, what the behavior was like at the beginning. operant level is the same as baseline. When the operant level is measured in rate, it is also the same as base rate.

3) The strength (e.g., rate or duration) of behavior prior to any known conditioning. (Baseline, which subsumes operant level, refers to the strength of behavior before the introduction of an experimental variable but does not preclude earlier conditioning.) 10

4) The baseline level of an operant, or the rate at which responses occur before they have been reinforced.

5) The rate of responding before reinforcement.