The target paper by Barba (2012) raises issues that were the focus of the author's first two publications on operant variability. The author will describe the main findings in those papers and then discuss Barba's specific arguments. Barba has argued against the operant nature of variability. (Contains 2 figures.)

In his article, the author claimed that studies of operant variability that use a lag-"n" or threshold procedure and measure the obtained variability through the change in U value fail to provide direct evidence that variability is an operant dimension of behavior. To do so, he adopted Catania's (1973) concept of the operant, which takes the…