There are 5 levels of evidence.

Level- 1 Highest Rank- determined by Random Control Trials (RCT) e.g. used in drug testing
Level -5 Lowest Rank e.g. Expert Opinion.

Sometimes we know things work but are not well tested. e.g. Jumping out of a aircraft with with a parachute has a better outcome then jumping without a parachute! This is only level 4 evidence or a case study.

Some Physio treatments work but lack good evidence at this point in time. Nevertheless, information provided from evidence based treatments is important to help the general public decide between science and advertising (spin).