Are Crew Resource Management (CRM) and other Human Factors methods effective?
A student of mine, who has a background in industrial engineering and is an emergency medicine physician, has morphed his career to include the application of CRM into emergency medicine and operating room procedures.  The health industry has in general been moving that way because it is saving lives and lawsuits.

Several people have published retrospective analysis of aviation accidents, which tend to contrast the kinds of errors which occurred prior to CRM, and the changes in flight deck politics.  

Military team operations, firefighting and other industry segments have started incorporating CRM into their training, and with measurable result.

Much of CRM today was developed  in response to significant aircraft disasters in the 1970's coupled with research at NASA and some universities which provided more insight as to how crews work together.  As an example, the unquestioned authority of the senior captain, was a factor in an alarming number of major accidents.  That protocol has been substantially replaced with a more collaborative protocol, and there are fewer accidents involving the same aspects of flight crew dynamics.

The medical application paper referenced below probably has statistics and material you might find particularly useful in your training.

Journal Articles:
https://www.tandfonline.com/doi/abs/10.1207/s15327108ijap0104_3

A medical application reference which talks about lessons learned in aviation:
https://www.emsreference.com/printpdf/47

A scholarly critical data driven analysis:
https://apps.dtic.mil/dtic/tr/fulltext/u2/a502230.pdf


  Technological advances continue to attempt to improve reliability and safety in
  aviation. Design considerations throughout the acquisition process must also continue to
  expound on integrating humans, including our cognitive and physiological capabilities, as
  fundamental aspects of aviation systems. Nevertheless, CRM training continues to be the
  primary method in mitigating the number of mishaps due to human crew coordination
  error in aviation. The program must go beyond simple training requirements and become
  more in grained into the culture. Perhaps the evidence found in this study suggests a
  transformation of cultural acceptance is gradually occurring.