Factorial design. This graphic shows the idea of a synergistic effect that only occurs in the verum-verum-group D (combination of both interventions). Furthermore, it shows how to calculate the synergistic effect. Group A = PLC + sham-rTMS; group B = PLC + real-rTMS; group C = ATX + sham-rTMS; group D = ATX + real-rTMS. X indicates interaction factor “ATX x real-rTMS” (synergistic effect).