The lack of evidence can be attributed to a lot of different things, but primarily it can be blamed on the amount of time and money it takes to carry out a research study. Also, we don't have enough people trained in research to perform the studies. Since many programs are only a couples years, that isn't enough time to carry out a full research study and it isn't enough time to train individuals on how to adequately perform larger research studies on their own. Also, we don't have many research doctoral programs where they are focused on OT. Students often have to get a research degree in psychology or another field and then apply it back to OT. Most OTs work as a practitioner and rarely will a job pay for the individual to take time out of their work day to perform research, so that adds an additional challenge.
We need evidence because the health care system demands proof that an intervention works or it may not pay for it. It is good because it makes sure that a health care worker isn't abusing the system and working outside of the realm of their expertise, but it can also stifle creativity and flexibility in treatment. The AOTA has started focusing more on it now because it recognizes the disparity in research and is trying to encourage more OTs to invest in a research doctorate and to consider entering into research. I believe a lot of why it wasn't happening from the beginning is because there wasn't anyone to teach it.
