VoltaicCell20 - Oklahoma State University–Stillwater. Minimizing Waste and Encouraging Green Practices 159 norm. In TPB, an extension of TRA, Ajzen added a new independent variable known as perceived behavioral control. Best corel painter 2015 brushes download 2016 free and torrent. Although both TRA and TPB describe intention as a mediating variable that impacts the actual behavior, past studies tended to examine intention as an approximate measure of behavior.