I think the studies were bias; an ITF school trying to prove that SW is better. Did anybody in the study actually hit harder without SW? And that after all the punches were done they just averaged it? I would be more readily to believe such a thing if the participants were all of equal height and weight. All had equal years of practice in their arts and included ITF, WTF, Karate, Boxers, etc. In fact the boxer probably could hit harder which than I guess would prove that all other punching arts are less; correct?
The bias in the study was not so much that the school was trying to prove that SW is better, the bias was in using only ITF practitioners who were used to doing the sinewave so were naturally better at it than using the hip twist.